It's not exactly the type of dress you would expect to see a pregnant mother wearing.

But actress Billie Piper raised eyebrows after she donned a racy sheer grey dress to attend an engagement at Capital Radio.

The young starlet's growing baby bump could clearly be seen through the revealing lightweight frock which left little to the imagination, as she posed with breakfast show hosts Johnny Vaughan and Lisa Snowdon.

And along with its plunging neckline, six months pregnant Billie's daring look could set a new trend for maternity wear.

Barely there: Billie Piper reveals her growing baby bump in a sheer grey dress with a plunging neckline in London today

The actress attended a radio interview at Capital Radio with breakfast show host Johnny Vaughan and co-host Lisa Snowdon

Billie Piper covers up her bump with a scarf as she leaves Capital's studios

Speaking about her pregnancy recently, Billie revealed she is mildly apprehensive about the birth, and has become fanatical about having scans.

'Some women are all about this glowing, blooming thing, aren't they?' she told The Observer.

'I haven't really tapped into that. I've basically replaced all my vices for a new one - control.

'I've had about 10 scans and I bought one of those baby heart monitor things. Such a bad idea - its like listening to a huge shell on the beach.

'But I do love it. The whole thing is just so sweet, tender and adorable.'

The 25-year-old actress who is married to actor Laurence Fox has kept herself busy throughout her pregnancy, filming the entire second series of raunchy ITV drama Secret Diary Of A Call Girl, despite the fact that she felt like a 'sweating sea cow' for most of it.

‘I found the heat very uncomfortable,’ she revealed. ‘I was thirsty all the time and always needing the toilet – which is really unhelpful when working to such a tight schedule!’

'I needed two body doubles in the end. As I got more and more pregnant I began to gain weight so it looked silly having a really skinny body double.'

The second series of the show, which is a big hit in the US, begins next month.

Billie looks set to name ex-husband Chris Evans as her baby’s godparent.

The actress split from the Radio 2 DJ in 2004, following a whirlwind three year romance.

However, the divorce was amicable with Billie making no claim on his estimated £30million fortune.