Home Secretary David Blunkett has said he is "deeply concerned" by the security breach which allowed a comedian to gatecrash Prince William's 21st birthday party at Windsor Castle.
Barschak was said to be trying to promote his comedy show
He is to make a statement to the Commons on Tuesday after considering a six-page report on the incident by police.
Self-styled "comedy terrorist" Aaron Barschak, dressed as terrorist leader Osama bin Laden in a pink ball gown, scaled a wall at the castle and talked his way past police.
He then mingled with guests including senior royals before jumping on stage as Prince William made a speech.
HAVE YOUR SAY
Perhaps some basic observation training wouldn't go amiss!
Police have apologised to the Royal Family over the incident, which Scotland Yard Commissioner Sir John Stevens described as an "appalling" breach of security.
The Tories are angry that the home secretary has chosen to speak to the media before making his statement.
Mr Blunkett says he wants to see that "lessons are learned" from the incident.
'Heads on block'
Asked if heads would roll over the security breakdown, the home secretary said: "There is no question that after what happened, everyone in every position all the way through counter-terrorism forces and royal protection know their heads are on the block.
"I'm not at the moment looking for scapegoats, I am looking for answers to very difficult questions."
I think we deserve better from those who are employed to look after our interests
Despite the need to re-assess security of the Royal Family, Mr Blunkett said he was confident the Queen and other Royals were safe.
Shadow home secretary Oliver Letwin said it was outrageous that MPs had to wait for a statement.
"I put down an urgent question today asking the Home Secretary to make a statement in the House of Commons. He has chosen instead to make a statement to the press."
In a point of order in the Commons, shadow leader of the House Eric Forth added: "Is this yet again not a defiance of Mr Speaker's rulings that ministers should not go out and tour the media studios before they come to this House of Commons to give an account of themselves?"
Metropolitan Police Assistant Commissioner David Veness said Mr Barschak had climbed a wall before convincing police at a check point that he had a genuine reason to be there.
"It's a combination of gaining access via an embankment, climbing a tree, jumping on to a wall and then reaching a terrace.
"He then appears to have approached a member of staff of the contractors, who then took him quite properly to a police point.
"He then proffered what must have appeared to be a credible story and regrettably gained access to the area where the party was taking place.
"I understand he indicated that he had reason to be present though the detail is a matter for the criminal investigation and the subsequent internal inquiry."
Asked how close Mr Barschak had been able to get to the Royal Family, Mr Veness said: "In our judgement and with our duty for royal protection there is no such thing as an acceptable proximity."
Senior Met and royal protection officers have already met to "draw out early lessons" from the security breach.
Mr Barschak was arrested inside the castle after mingling with 300 guests, including all the senior members of the Royal Family except Prince Edward, at the Africa-themed fancy dress party.
The comedian told the Sun newspaper: "It was unbelievably simple. I'm amazed I got in. Royal security is not at all what I expected."
Mr Barschak was apparently trying to publicise his Edinburgh Fringe Festival comedy show by dressing up as Osama Bin Laden, according to his father Fred Barschak.
The comedian, from London, was questioned at a Thames Valley police station before being put into the custody of the Metropolitan Police on Sunday.
He was released on bail and is due to return to a London police station next month.
A St James's Palace spokeswoman refused to comment on how the incident had affected the Royal Family and other party guests.