The Queen woke to find the man there and talked calmly to him for several minutes before taking the opportunity to call a footman when the man asked for a cigarette.

And the Sun today reports that the intruder had made at least 12 visits to the Palace, telling his wife that he was off to see his "girl friend - Elizabeth Regina." According to the paper, the man's mother spoke of her son's "girl friend called Elizabeth living in SW1."

She went on: "He said she had four children, like him, but was a bit older than he was."

The man's father, aged 53, said his son was a "royal fanatic," and went to the Palace "just to prove how easy it was to get in. He would not harm a hair on her head," he added.

"He was a very happy-go-lucky person and I think he would have put the Queen at ease straight away. He could smooth-talk anyone."

According to the Sun, the intruder is 31 with four children aged between 10 and three. His mother was quoted as saying of her son: "We knew he had trouble sleeping at nights, and often went out in the early hours. But no-one had any idea where he was going."

His sister is quoted as saying her brother paid his last but one visit to the Palace last week before he was caught early on Friday morning. "He had been away all night and when I asked him what he had been up to, he told me with a broad grin: 'I've been to see my girlfriend.'"

The Home secretary, Mr William Whitelaw, told the Commons yesterday that he was shocked and staggered by the serious failure in security arrangements.

He said he had already set up an urgent inquiry into the incident under Mr John Dellow, an assistant commissioner at Scotland Yard, and he had received the first interim report of the inquiry before making his statement to the Commons.

The Director of Public Prosecutions is expected to bring charges against the intruder.

On Saturday, the day after the incident, Mr Michael Fagan, of no fixed address, appeared in court, accused of entering Buckingham Palace on June 7 and stealing half a bottle of wine.

Asked by the Opposition spokesman, Mr Roy Hattersley, whether the same man was involved in both incidents, Mr Whitelaw said it would be wrong for him to answer or to discuss any further details at a time when there was a possibility of charges.

But a later exchange in the House of Lords clarified the point. Lord Elwyn-Jones asked the Government spokesman, Lord Elton: "Are we talking about two men, or is it one man and the same man? As I understand it, it was two men, but I think the public would be anxious to know if this is so."

Lord Elton replied: "The man about whom allegations are now being made is the man who was charged for the original offence."

Mr Whitelaw admitted that additional security measures at Buckingham Palace had not proved satisfactory, and that immediate steps had been taken on Friday to strengthen security around its perimeter.

He told MPs that the inquiry will have to look not only at Buckingham Palace but at the security arrangements for all other royal residences and for "all people in positions of vulnerability."

The incident has clearly been a profound embarrassment to Mr Whitelaw, who has often found himself under fire from his own backbenchers on the sensitive issue of law and order.

Yesterday he had to agree with Sir William Clark, a senior Tory backbencher, when he said that the result could have been catastrophic if it had been a terrorist who had found his way into the Queen's bedroom.

But it was Mr Hattersley who scored a bull's-eye when he asked about the additional security measures introduced at Buckingham Palace over the last 18 months.

"Since that resulted in a man getting into the Queen's bedroom," he said, "how bad was it before the improvement?" He welcomed the inquiry and said the whole House was relieved that the incident had ended with no hurt to the Queen.

But it was absolutely crucial to establish what steps were taken to improve security at the Palace.

"Was it necessary for the Daily Express to enjoy their extraordinary scoop before the situation was taken with the seriousness it warrants?"

Mr Whitelaw confirmed that there had been a review, and that the result of the review had been substantially carried out. "But this latest incident shows that the position is still not satisfactory," he said.

This was greeted as the under-statement of the year by the former Labour minister, Mr David Ennals, who said that the public was "really very shocked and staggered that this event could have occurred."

The man entered by scaling the 14ft perimeter wall, topped by revolving spikes and barbed wire added after a series of recent intrusions. He somehow avoided a web of sensors and trip wires which were thoroughly checked last year and then went undetected by the police and dog patrols which are supposed to scour the grounds. Then he shinned up a drainpipe to get into the Palace.

His penetration of the private apartments is unprecedented since Queen Victoria's reign, and defied another network of wires and beams which theoretically sound an alarm at Scotland Yard if anyone makes an unauthorised entry through any door or window.

There have been six serious incursions at the palace in the past year. In June 1981 three German tourists camped in the grounds under the impression they were part of Hyde Park; in August a man was found in some bushes professing admiration for Princess Anne; in September a youth was arrested at the palace gates with an airgun; in December a mentally ill man was found in the grounds, and last month a man with an 8-inch dagger pushed past police into the grounds.

Historically, royalty has always been vulnerable to lone wolves, and the present Queen Mother came as close to an intruder during the war as her daughter did last week. She surprised an Army deserter in her private bathroom at Windsor Castle and gave him a lecture on duty before calling for the castle guard.