Britain's Watergate – or just leaky security? The mystery of the Commons break-in

Checks under scrutiny as rumours swirl that Miliband office breach was 'inside job'

The door to EdMiliband’s offices was reported to have been forced open (PA)

Is Ed Miliband's suite of offices in Westminster about to become the British Watergate? Only if a forced door, scattered papers and someone "messing about" with a computer are evidence of a covert burglary at the heart of Britain's parliamentary democracy.

Click here to see the 'Ring to steel? - Westminister's security'

Scotland Yard is remaining neutral on what happened last Friday at 7pm when the door to the Labour's leader's suite of offices in the Norman Shaw South annexe was reported as having been forced open.

The Metropolitan Police will say only that its inquiries are on-going. Westminster sources say Mr Miliband's team does not know if anything has been taken, therefore it can't say if anything "sinister" has happened.

With tabloids already placing spymasters and Special Branch at the crime scene, and allegations swirling of a "dirty tricks" campaign ahead of this week's Budget, the pressure for NormanShawSouthGate is building.

Palace of Westminster security officials are more pragmatic. A re-examination of the entire parliamentary estate's security is being undertaken. The review will include examining security at the main entry points to all the parliamentary buildings, with a potentially expensive upgrade of the entry pass system not being ruled out.

The Speaker, John Bercow, will be embarrassed that a year on from the foam pie attack on Rupert Murdoch, which took place in one of the first floor committee rooms in Portcullis House, security is once again in the headlines.

How a potential thief reached the second-floor offices of the Opposition – which also include the private office of the shadow chancellor, Ed Balls – is being looked at by the Met.

From Portcullis House – which can be accessed from the main Palace of Westminster, from entrances at Derby Gate and the Victoria Embankment, and via a special pass-holders-only entrance inside Westminster tube station – stairs and a walkway lead to the Opposition offices overlooking the Thames. One insider said: "These offices won't be found by chance. Someone who didn't know their way around would find it difficult. This suggests a pass-holder."

Without a pass, entry is difficult. There is substantial police presence at the entrance next to Black Rod's Gardens. The members' and visitors' entrance at Cromwell Green is equally secure, with the underground station entrance requiring a pass code entry supervised by police.

The Derby Gate entrance on Whitehall gives fast-track access to Portcullis House. Entry here should mean going through the security room and access through Portcullis. However those leaving the building do not have to pass through the same security regime, with police also concerned about the vehicle access which is possible here.

The Met has been tasked with assessing who was near the Norman Shaw annexes during the time of the alleged break-in. However the lack of CCTV coverage and the fact that pass holders do not need to check out when leaving the parliamentary estate, makes that task almost impossible.

The mood in the Opposition offices is said to be "concerned". However, with nothing missing and Mr Miliband's private inner office not touched, other MPs and journalists say the door-forcing is more likely to be part of a growing problem that has seen five computers stolen from the media offices in the past few months.

With 25 laptops disappearing last year, along with 40 reported incidents of theft that included iPads and mobile phones, honesty, as one official put it, "is a problem that stretches beyond MPs and their expenses".