It is a fascinating tale of two men and a diary. Yet the one absolute certainty is that Alan Clark, Tory MP and acerbic diarist, is not the author of Alan Clark's Secret Political Diary as serialised by the London Evening Standard.

After the thousands of words written by Mr Clark in his own political diaries, this week it was the task of lawyers in Court 60 at the High Court in London to argue about the merits, or otherwise, of a spoof diary that has pricked Mr Clark's "colossal vanity".

The Secret Diary, written by Peter Bradshaw under Mr Clark's photograph, appeared in the newspaper soon after Mr Clark's election as MP for Kensington and Chelsea in May. With such delightful gems as "Sinead is quite strict, which I like, with long dark hair and a charming lilt to her voice. Emma is behind, in wig and gown, frowning prettily over her submissions", the Diary has nonetheless embarrassed Mr Clark, who fears the public will believe he wrote it.

By any standard the spoof diaries are a hoot. Mr Clark's style as a diarist and his love of women are parodied by Peter Bradshaw with an alarming degree of accuracy. Mr Bradshaw's Clark is portrayed careering down the streets of Kensington and Chelsea in a fast car, musing on the delights of the women in his constituency and the latest intake of Blair's babes in the House of Commons.

In his own diaries, Mr Clark referred to Dame Janet Fookes MP as "having a vast arse", while Tom King was a "ghastly and awful person, blustering, bullying and stupid". Only beautiful young women were the targets of his admiration, but the stricter they were, the better for Mr Clark! And of course his love of Lady Thatcher's ankles is a recurring theme.

For his part, Mr Clark has not seen the funny side and is suing the Evening Standard for damaging his reputation. The editor of the Standard, Max Hastings, has accused Mr Clark - the man who "loves to be famous and loves to be naughty" - of not being prepared to be teased, especially as he says Mr Clark "has always encouraged and thrived on publicity".

The unhappy relationship between Mr Clark and the Evening Standard was not always so. In fact, it emerged in court this week that Mr Hastings had approached Mr Clark about penning a genuine diary column after Peter Bradshaw's first piece was published. However, in a flurry of correspondence between Mr Clark and Mr Hastings, during which they haggled over payment, Mr Hastings was eventually forced to issue a mild reprimand to his friend.

After Mr Clark had refused his offer of £60,000 a year to write the column, Mr Hastings rushed off a reply stating: "There is no way we could come within a million miles of the money you are asking. You have to gaze at the ceilings of a lot of very rich newspaper proprietors to get that sort of dosh."

The spoof diaries continued to appear under Bradshaw's tiny by-line, and back in court this week a succession of Tory MPs and constituents claimed they had been fooled into believing Mr Clark had written them.

One woman, a constituent, told the court the diary confirmed her belief that he was "a very nasty piece of work". She had only decided to read the newspaper because she did not have her library book with her, but she was not happy with what she read. As an MP, she remarked, he had not held up traditional family values and, prompted during cross-examination to elaborate on an MP's credentials, she explained it was not enough to be a proper Christian with 2.4 children, an MP must also have a dog.

When Mr Clark stepped up to take his turn in the witness box on Tuesday the spoof diary described the event as a "glorious day" during which "Mr Clark" realised that he was "quite unscathed" by the weapon unleashed by "the enemy". In Court 60, the real Mr Clark was cross-examined about his extra-marital affairs and his "sexual vanity". Asked if he was somewhat obsessed with his physical appearance, his physique and sexual attractiveness, the reply was Clark at his vintage best.

"Self-assessment is difficult enough in doing one's income tax, I think in relation to character it's quite valueless."

For the man once vilified by his own party for his comments about disposing of the IRA, Mr Clark was accused this week of displaying a distinct lack of humour about his image. Instead of being described as a "Don Juan with a twinkle in his eye" the spoof diaries mocked him as an "ancient roue with a penchant for attacking sanctimonious political colleagues".

Whether the spoof diary is proved to be an example of the finest tradition of British journalism, as the Evening Standard believes, or a preposterous" comment upon Mr Clark's character, his reputation for "general naughtiness" is safe.

In the words of "Mr Clark" this week: "I sense that the hour of ultimate victory is at hand . . . I came face to face with little Bradshaw outside the court first thing, giving an icy, curt nod. I imagine that he has been held overnight in the Paddington Green police cells and hustled in under a blanket. However, I was dismayed that he did not have to appear between two policemen - and no handcuffs. Pure intimidation."

The case continues next year.