A prankster sparked an urgent inquiry into security surrounding the Royal Family after he gatecrashed Prince William's 21st birthday party dressed as Osama bin Laden.

Home Secretary David Blunkett ordered the inquiry after stand-up comedian Aaron Barschak was able to slip past tight security at Windsor Castle and climb on stage while the Prince was making a speech.

Although Barschak's father, Fred, insisted last night that his son would not have meant any harm, shocked Government officials were left asking: What if he had been a terrorist?

Police would not confirm the man's identity but said a 36-year-old man from London had been arrested on suspicion of burglary, which covers unauthorised people entering premises.

Last night, he was bailed to return to a London police station on a date next month pending further inquiries.

Mr Barschak, 72, said he recognised his son as the man being led away by police following the security breach.

The property developer from Kilburn, north London, said his son was probably trying to publicise his act.

The comedian regularly dresses up as the notorious al Qaida leader and goes under the name Comedy Terrorist.

His previous targets have included London Mayor Ken Livingstone and comedians Terry Jones and Graham Norton.

Mr Barschak said: "He would not have been trying to harm anyone, not at all. He is actually not at all anti-royal.

"He is a professional stand-up comedian who is desperate to be a serious actor."

Mr Barschak added: "I do worry about my son. With security as it is at the moment you just have no idea what might happen next."

Before gatecrashing Prince William's celebrations, his son was seen outside Windsor Castle dressed in a pink dress, turban, sunglasses and false beard as guests arrived for the much-publicised party.

Guests had donned fancy dress in keeping with the Out of Africa theme for the event, including the Queen, the Prince of Wales and the majority of the Royal Family.

At the time, Barschak shouted to reporters and the watching crowd: "Happy birthday. Out of Africa, I'm out of this world."

He then went on to publicise his performances at the Edinburgh Fringe Festival in August.

During his bizarre speech he lifted up the front of his dress to reveal another false beard and declared: "The real hair to the throne."

He was led away from the crowd by a uniformed policeman and wandered off towards Windsor town centre.

A Home Office spokeswoman said Mr Blunkett had ordered an immediate review of the incident, to be led by police and security advisors.

A further, more in-depth inquiry might be ordered depending on the outcome of the initial review of events.

A spokesman for the Metropolitan Police said: "We consider any breach of security to be a serious matter and a thorough review into all the circumstances surrounding the incident is under way."

The News of the World reported that the man stumbled on to the stage where William was making a speech and grabbed the microphone before security guards and police pulled him away.

William was said to have attempted to lighten the mood by later reclaiming the microphone and joking: "I didn't know my brother could do an accent like that."