London:  A serial burglar conned his way into Downing Street and got within yards of the Prime Minister's office by showing his girlfriend's Lithuanian ID card to a security guard.

Obadiah Marius strolled into the Cabinet Office building in Whitehall then wandered unchallenged around a number of unmanned offices used by Cabinet Office and Privy Council officials last June.

It is understood he walked near the Cobra emergency room where the Prime Minister coordinates the response to anti-terrorist emergencies and was close to the then Prime Minister Tony Blair's personal office.

Marius was only arrested and armed police called when he wandered out of No 9 Downing Street.

He was on bail at the time, having entered the judges' chambers at Snaresbrook crown court to steal three laptop computers worth £4,500 (Dh33,300).

Marius, 43, has 78 previous convictions for offences committed to feeding his drug habit and has spent most of his adult life in prison. Six years ago he attempted to break into the TUC building in Crouch End Hill and specialises in burgling public buildings including theatres, schools and shops.

But despite his appalling record Judge Christopher Hardy yesterday decided to give him "one last chance" and handed him a suspended sentence and a residential drug rehabilitation order.

Isobel Ascherson, prosecuting, told Southwark crown court that Marius and his girlfriend, 19-year-old Victoria Smith, walked into the Cabinet Office at No 70 Whitehall. The security guard on duty later told police that Marius "may have held up what I believed to be a building pass".

But the only security card the couple were later found to be carrying was Smith's Lithuanian photo ID pass.

Ascherson said: "The doors marked ministers were either unlocked for him or were not properly locked.

"In what was quite an astonishing breach of security this man and his girlfriend were let loose in the Cabinet Office at around 6pm."