Police are investigating whether a fugitive armed robber known as the ''Skull Cracker'' has struck again.

Michael Wheatley, 55, went missing when he was released on a temporary licence from an open prison in Kent on Saturday, and has since been seen in Twickenham, south west London.

Today a branch of the Chelsea Building Society in Sunbury-on-Thames, Surrey, was robbed, and Surrey and Kent Police are trying to find out whether Wheatley is the culprit.

He was given 13 life sentences in 2002 for a series of brutal raids on banks, and is one of more than 1,200 open prison inmates serving an indeterminate sentence.

He was ordered to serve a minimum of eight years before being eligible for consideration for parole.

A spokeswoman for Surrey Police said: ''At 10.20am today Surrey Police responded to reports of an armed robbery at a building society in Sunbury. The incident took place at the Chelsea Building Society at The Parade, Staines Road.

''Officers including specialist firearms officers are currently at the scene. Anyone with information or who witnessed the incident and has not already spoken to police should call 101.

''The investigation is in its early stages. We are carrying out numerous inquiries to identify the offender and have linked in with Kent Police as part of these inquiries.''

Wheatley was released on a temporary licence from HMP Standford Hill open prison on the Isle of Sheppey, Kent, and is thought to have boarded the 9.20am high speed train from Sittingbourne, which was heading to Stratford International station.

Police were called when he failed to return to the prison at 6pm and a specialist team of officers, headed by Detective Chief Inspector Ann Lisseman, pieced together a timeline of his movements since his disappearance.

There was a confirmed sighting of Wheatley at 7.55pm on Monday in the Strawberry Hill area of Twickenham, and several homes were searched but he was not found.

Kent Police said Wheatley, who earned his nickname after pistol-whipping victims, including a 73-year-old woman, has connections in Ireland, Cheshire and North Wales.

Earlier Sir David Calvert-Smith, chair of the Parole Board, which carries out risk assessments on prisoners to determine whether they can be safely released into the community, defended the decision to allow Wheatley out on day release.

''I think putting all prisoners in open conditions is an essential step to their integration. Otherwise, we as a society simply have to put up with paying for their accommodation in prison for the rest of their lives,'' he told BBC Breakfast.

''There has got to be a system which manages the transition from prison to the outside world.''

Sir David said ''decisions are not taken lightly'' if a prisoner tells the board they have left their violent past behind them.

''We cross-examine the prisoner to see if he's simply paying lip service,'' he said.

''What we are not testing is whether he is likely to escape. What we are concerned with is the risk to the public of serious further crime.''

There are currently only 45 to 50 people who are condemned to serve whole-life sentences, meaning that every other prisoner is forecast to be released at some stage, he added.

A spokesman for Kent Police said: ''Officers searching for Michael Wheatley are aware of a robbery which took place today at a building society in the Surrey Police area. Kent Police is working closely with the Metropolitan Police Service and Surrey Police as part of ongoing inquiries.''