Guilty: the decorator who masqueraded as a celebrity, a TV presenter and a royal detective

To his acquaintances on London's party circuit, he was a polo-playing millionaire with a £105,000 Mercedes, a string of celebrity girlfriends and the photographs to prove his friendship with the Prince of Wales and Prince William.

But in reality, Michael Hammond was a decorator's son from Sussex whose skill as a conman allowed him to trick his way into Windsor Castle and spend an hour wandering freely in the grounds. The 36-year-old was only arrested when security cameras picked up a stranger in the gardens talking into a mobile phone and wearing ripped jeans and a jumper.

Isleworth Crown Court in west London, heard yesterday that Hammond had used the phone to call police at the castle pretending to be Detective Superintendent Simon Morgan, a real Scotland Yard officer leading the hunt for a prolific sex attacker. Using Det Supt Morgan's name, the conman explained he was accompanying famous friends of Prince William and Prince Harry who wished to avoid being seen.

When he arrived at the Henry VIII gate, the entrance used by members of the Royal Family, Hammond and a girlfriend were waved through.

The ruse was one of dozens of incidents over six months last year in which he impersonated a police officer.

Hammond yesterday admitted a single charge of being a public nuisance which incorporated 11 counts of pretending to be a police officer and one of wasting police time.

The court heard that the "fantasist" caused officers to be diverted to "incidents" ranging from a search for armed suspects near Downing Street to the interception of an Iraqi family on a car ferry on the grounds they were al-Qa'ida suspects.

Anthony Connell, a spokesman for the Crown Prosecution Service, said: "His deceptions have deprived the people of London of the services of many police officers for lengthy periods of time when Londoners were under threat of terrorist attacks. He has also caused many innocent people, including members of ethnic minorities, to be detained by the police, often at gunpoint. He is a dishonest and wicked man."

Although no members of the Royal Family were in residence at Windsor at the time of his deception, Hammond's escapade exposed fresh failings in security at the castle, where a self-styled comedy terrorist gatecrashed Prince William's 21st birthday party in 2003.

The incident on 17 May last year was just one in a series of deceptions. A regular in London's glitziest night spots, Hammond falsely boasted of love affairs with famous women including the singer Dannii Minogue and the glamour model Jordan.

Tall and dark-haired, he was photographed by paparazzi and using a false double-barrelled name, Edwards-Hammond, he featured regularly in newspaper gossip columns.

Among the phrases used to describe him to readers were "film consultant", "theatre producer" and "Brit smoothie".

To back up his claims to know Prince Charles and William and Harry, he produced photographs of himself next to them at polo events. He even succeeded in persuading television producers of his connections, fronting a programme for Sky Sports about the polo event sponsored by Cartier at Windsor Great Park.

But when police searched Hammond's luxury penthouse, they found his Mercedes had been obtained by deception and he was in such severe debt he could not pay the bills on his rented home.

A police analysis of his phone records found he had called officers 133 times between September 2003 and last August.

On one occasion in February last year, he called City of London Police to claim he was a leading surgeon called Dr Eli Silva in need of an escort convoy to perform a life-saving operation on a child. After the escort had driven on the wrong side of the road and stopped traffic, Hammond phoned the next day to thank officers. In another incident, he pretended to be another Yard detective and claimed he had seen three black men, one with a hand gun, acting suspiciously at a McDonald's near Downing Street. Armed officers and a diplomatic protection unit were dispatched and three men were searched at gunpoint.

Even after his arrest following the Windsor Castle incident, Hammond continued his impersonations, the court was told. While travelling on a car ferry to Dover, he pretended to be from Interpol and had an Iraqi family stopped and searched after claiming he recognised them from a list of al-Qa'ida suspects.

Hammond, who was remanded in custody and has previous convictions for impersonating police officers, will be sentenced next month.