Undercover Mirror journalist exposed as she tries to infiltrate Tory Party

In the latest sign that the embattled Conservative leader is determined to get tough with his media critics, an undercover journalist was exposed by party chiefs in a humiliating showdown.

Emily Miller, 25, who claimed to work for a charity that helps Indian children, applied for a £40,000-a-year job as assistant to Conservative Party chairman Caroline Spelman.

She said she wanted to help Mr Cameron to defeat Gordon Brown at the next Election. But her real aim was to spy on the Conservatives' Election plans and to help Labour win a fourth term.

Ms Miller was caught out when the Tories discovered her Hotmail email account was linked to the Daily Mirror, Labour's main cheerleader in Fleet Street.

When officials confronted her at party HQ on Friday, she said "I have been rumbled' and fled the building.

The exposure comes only days after Mr Cameron forced the BBC to apologise for insulting John Redwood, author of the Tories' new tax-cutting blueprint.

It is the latest sign that he is fighting back hard following fears among Tory MPs that their inexperienced leader is being steamrollered by ruthless Mr Brown's battle-hardened Labour campaign team.

Ms Miller came close to pulling off a spectacular coup. Impressed by her classic, and mostly genuine, Tory-style CV, including an education at Cheltenham's Pate's Grammar School and St Edmund Hall College, Oxford, skiing in Austria and a Duke of Edinburgh Gold Award followed by charity work, she was set to be given a key job in Mr Cameron's Election HQ.

But she omitted to mention one critical fact - her burgeoning career as an ambitious young journalist, with TV and Fleet Street experience already under her belt.

With a desk in Ms Spelman's private office, Ms Miller would have had access to secret Tory documents and been privy to confidential discussions between Mr Cameron and other party leaders.

Placed as a "sleeper", she would have been able to provide a series of well-timed leaks in the run-up to the Election and reveal tensions in the Tory high command.

She wrote on her application form: "Much of what David Cameron has said about social responsibility rings true with me. It gives me enthusiasm to work as hard as I can for the Conservative cause."

But officials grew suspicious when they checked her references. One man named as Ms Miller's manager at the charity, Asha, which helps poor Indian youngsters, did not appear to exist.

Further investigations revealed that a reporter named Emily Miller had written articles for the Daily Mirror.

Ms Miller's cover was finally blown when a party computer expert established that her application form was sent from a Hotmail address accessed from a Daily Mirror computer.

In her third and final interview on Friday, Ms Miller praised the Conservatives' tax proposals announced that day, saying: "I am very encouraged by the policies you are putting forward on tax. My own political views are centre-Right so I like what you are doing."

Initially she denied working for the Mirror but, when asked why her application was typed on a Daily Mirror computer, she owned up to the scam and fled.

A Tory spokesman said: "We vet all applications with the utmost stringency and it is extraordinary that the Daily Mirror thought they could get away with this. We suspect there have been other recent attempts to infiltrate the party.

"It is a pity executives on the paper saw fit to use this young woman to carry out such a sinister act of deception."

Ms Miller and the Daily Mirror declined to comment yesterday. Four years ago, the Queen fell victim to a similar Daily Mirror stunt when one of its reporters got a job as a Buckingham Palace footman and described how he served her breakfast.