Sunday morning at the three-storey Georgian town house in North London where GMTV presenter Kate Garraway lives with her husband Derek Draper - and the sound of wailing and gnashing of teeth can probably be heard by half of Islington.

The source is not their two-year-old daughter, Darcey, throwing a tantrum, but Miss Garraway herself, who is experiencing a spell of very public humiliation - all thanks to her colleague, Fiona Phillips.

'Fiona has really knifed me,' she complained to a friend. 'What on earth am I going to do?'

Red vs Blue: The battle between Kate Garraway and Fiona Phillips, which has simmered for years, is now in the public domain

Thanks to Phillips' very public machinations, poor Kate now has little room for manoeuvre.

Last week, Fiona announced she intends to step down after 12 years as the main anchor at GMTV, and gave an interview to a Sunday paper which amounted to a surprisingly open attack on her younger, more glamorous colleague.

Garraway, 41, has been at GMTV for eight years and was widely expected to be given Phillips's job. But she found herself very publicly described as shallow and attention-seeking.

Miss Phillips also pointed out that Kate had not been in touch to wish her well - although given the state of their relationship, it would have been rather odd if she had.

'She is probably quite pleased I am going,' said Fiona, 47. 'I have the top job. It wouldn't be natural, and she'd be lying, if she said she didn't want it. It doesn't annoy me that I haven't heard from her. Nor am I basing any of my decisions on how she feels.'

Phillips then spoke about the provocative photograph of Garraway, which appeared to show her breastfeeding a calf, taken to promote a Channel 4 documentary.

'People handle things in different ways. But I have never done that, or gone to the opening of an envelope to get headlines and your picture in the paper. It's not how I operate, but it doesn't make me a good person and her a bad one.'

Ouch! Until now, the enmity which exists between the two women has remained out of public view. They have posed, smiling, arm-in-arm at public functions; they make carefully worded but complimentary remarks about each other in interviews.

But finally, as Fiona prepares to step away from the sofa in December, she has given us a glimpse into the world of jealousy and mistrust which exists between them.

And what elevates this from an entertaining spat into full-blown intrigue is the fact that Fiona is married to Martin Frizzell, the editor of GMTV. He will - presumably - have considerable say about who steps into his wife's shoes when she leaves the show, which attracts six million viewers every morning.

Is it fanciful to imagine Fiona is trying to make sure Kate is not the next Queen Bee of GMTV?

Professional friendship: Kate Garraway and Fiona Phillips have always paid each other carefully-worded compliments

Certainly, there seem to be no end of stories emerging that are harmful to Kate. Some suggest bosses would prefer Christine Bleakley of BBC's One Show for the prime sofa spot. Others say Ulrika Jonsson is in the frame. Another story claimed that Fiona actually turned down the breastfeeding programme which Kate made such a noise about.

No wonder Garraway's agent, Melanie Rockliffe, sounds so exasperated. 'Kate is in the middle of her contract and she is working as she always does,' she says. 'I don't see what else we can do.

'I don't know why people are so worked up about this when there are wars going on in the world. That's all I have to say on the matter, thank you.'

But some of the sources I've spoken to this week believe Kate is on the brink of leaving GMTV after the humiliating way she has been treated. She was not even warned by GMTV that Phillips was leaving: the first she knew of it was when she was called for a comment by a journalist.

Worse still, the press office briefed that Kate would carry on presenting on Thursdays and Fridays - a clear indication that she was not even in the frame for the main job,
presenting Monday to Wednesday.

This week, bosses would say only they were 'busy planning Fiona's leaving party' and had not really thought about replacements for her yet - which, if true, says something extraordinary about the way they manage their staff.

Well-placed sources say Kate's request for a meeting with GMTV executives to thrash out her future has been denied. She was told they plan to settle the succession question in November, and not before - meaning Kate has to stay quiet while her bosses may court rival candidates.

So what is the inside story of these two women, known by GMTV insiders as Fiona The Moaner and Calamity Kate? Why do they dislike each other so much? And why is Fiona really moving on?

Round 1: Fiona vs Eamonn Holmes

When Kate arrived at GMTV in 2000, Fiona was already the veteran of a bruising clash of egos with her then co-presenter Eamonn Holmes - a battle from which Fiona emerged victorious.

'Fiona is on a cushy number with GMTV,' a former colleague says. 'She tends to get exactly what she wants, which goes back to her days with Eamonn.'

When she joined the station, Holmes was the star and took the lead on big interviews or breaking news stories.

One person who worked on the show at this time tells me: 'There was a huge enmity between them - which all boiled down to jealousy. Eamonn was the established star and is a proper journalist. He's the sort of person who not only writes his own script but makes sure he is on time for all the ad breaks.

'Any big interview would automatically go to him, which made Fiona furious. She didn't want to be the blonde fluff - she wanted to be the Queen Bee and would complain endlessly to the bosses.

'She was also very jealous of the money Eamonn made from corporate gigs. I know Fiona pretty well and she is funny about money. It's very important to her.

'She is not the sort of person who is always buying a round of coffees for everyone from the canteen, but she has spent tons on her house and is very proud of it. Her bathroom taps were shipped in from Germany and cost something ridiculous, like several thousand pounds each.'

Holmes was in Fiona's sights, and it wasn't long before, as my source puts it, 'she saw him off'. How?

'She was best friends with Peter McHugh. They holiday together and have Sunday lunches. And, of course, she is married to Martin. In the end, executives got sick of Eamonn - by which time Fiona had made herself the face of the programme.'

Onscreen chemistry: GMTV presenter Fiona Phillips with co-host Eamonn Holmes worked very well in front of the camera, but tensions mounted behind the scenes

A friend of Holmes' confirmed this, saying: 'At first, Eamonn adored Fiona and told everyone she was wonderful. Then it came back to him, via the then editor Gerry Melling, that Fiona didn't think much of him.

'Fiona denied it when Eamonn confronted her - but from then on he hated her. He would complain about her constantly. He would describe her as "false as f***". He must have said that to me a million times.

'There was a huge act that they were chums. It is greatly to their credit that they were such a good partnership on screen, because offscreen there was nothing between them but distrust.'

Holmes revealed in his biography that Fiona's status as Frizzell's wife was awkward, to say the least. ' Martin Frizzell was controversially promoted from reporter to editor,' he wrote, 'and therefore became the boss of me and his wife.

'He didn't mess around, making his intentions clear from the start. A few weeks after his appointment, he told me he was winding me down from five days a week to four.'

When Holmes left, there was no one to challenge Fiona's eminence. And yet some say she has remained surprisingly insecure and takes care to watch her back.

Round 2: Enter Kate

This paranoia is evident from Fiona's relationship with Kate Garraway. A friend of Kate's told me: 'It's a terrible relationship. Fiona used to accuse Kate of leaking harmful stories to the press about her. Surprisingly, Fiona seems to be insecure about Kate and how well she is doing, and the kind of coverage she gets.

'Take when Kate was in hospital with kidney troubles. They suspected it could be cancer - but Fiona was not in touch at all. Similarly, when Kate had her baby, there was no card or flowers from Fiona.

'That said, I don't think that Fiona wants to stop Kate from getting the job - simply because I don't think it's within her power.

'The practicality for GMTV is very simple: ad income is down, the ratings aren't great, and they don't have the money to splash out £300k for a new face. So they are almost certain to give it to Kate.

'Anyway, the bosses aren't actually that interested in who presents the programme. Peter McHugh has said for years that the ratings are the same, no matter who is presenting it.'

Despite this, the war between the two grand dames of GMTV has been postively acidic. Last year, Kate moved out of the tiny dressing room she had shared with Fiona, with insiders describing a truly poisonous atmosphere.

Friendly team: Kate and Fiona and fellow presenter Andrew Castle together with Kate's newborn daughter Darcey

After Kate's performance on Strictly Come Dancing, where she was staggeringly inept but wildly popular, their relationship seemed to get worse, and so she began to share a room with newsreader Penny Smith, with whom she shared an agent, Jon Roseman.

Kate and Penny remain friends, and she also has an ally in weathergirl Lisa Aziz

Indeed, Kate tries rather harder than Fiona to be everybody's pal. While Fiona is noted for not sending Christmas cards, Kate - in an effort to network - has held large parties at her home for colleagues.

She is shrewd and driven, and known affectionately as 'Calamity' because of her vulnerable air and habit of making winsome appeals for help, which some feel are rather attention-seeking.

But beneath the sweetness, there is enormous ambition and great determination. You don't, after all, get a £400,000-a-year job just by being Little Miss Marshmallow.

Fiona, meanwhile, is known as Fiona the Moaner because that's all she's done ever since she had children (her sons Nat, nine, and Mackenzie, six). A great deal of her off-screen time is spent complaining, a la Cherie Blair, that she is not Superwoman.

Whoever loses, TV wins

Another former colleague said: 'Fiona may be paid £600,000 a year but she's always full of angst about managing everything.

'And there is no place on television like GMTV - it is the most toxic atmosphere to work in, a real battleground. How much time would you want to spend in that sort of horrible atmosphere?'

She continued: 'We had several long conversations about her mother, when she had Alzheimer's, and Fiona had a lot of guilt about not being able to be with her more. Maybe now she just wants it to be different for her father, who is elderly.'

What will Fiona do next? And who will fill her seat? The questions remain unanswered

Fiona's assertion that she needs to quit in order to devote more time to her marriage and to be less of a 'madwoman' when it comes to her husband also rings true to those who know the couple.

Fiona said: 'Our marriage has been on the edge. By the time he gets home at 8pm, I am completely frazzled and worrying about getting to bed.

'He has sometimes been desperate for my attention, but instead of listening, I say: "For God's sake. I've been up since 4am. Don't you understand how tired I am?"

'I know I've been a madwoman, but it is just the tiredness. It makes me see the dark side of everything.'

Her colleague agrees, saying: 'She and Martin have a very stormy relationship - they always have done - but in some way they are obviously good for each other.'

No wonder, then, that some of Fiona's colleagues cannot believe she is walking away from this well-paid job which she fought so hard to get and hang on to.

There are those who mutter about GMTV wanting a relaunch - a change of face to help wipe away everything associated with the phone-ins scandal which cost it a £2 million fine from Ofcom earlier this year.

Others speculate that Fiona's support for the Labour Party (she says she was offered a ministerial job and that she very much admires Gordon Brown) is not helpful in the presenter of a news programme.

But as much as she professes to hate the early starts and pressurised schedule, there can be little doubt that Fiona the Moaner will miss her spot on that famous sofa.

After all, she has worked so terribly hard to get there. And not even her very expensive bathroom taps will fill the gap that GMTV will leave behind...