The Government Gateway web site that allows businesses securely to interact with Whitehall services has reopened after the most recent government data loss forced the site to close for 24 hours over the weekend.

A memory stick was found in a pub car park that contained access passwords for the site, as well as some source code.

The £18m site, which is run by the Department for Work and Pensions, is part of the joined-up government initiative and allows businesses and citizens to pay taxes and access other government services online.

The USB memory stick was lost by an employee of supplier Atos Origin, which won the five-year, £46.7m contract to manage the web site in 2006.

The storage device was found two weeks ago outside a branch of the Brewers Fayre pub chain in Cannock, Staffordshire. It was handed to the Mail on Sunday, which handed it on to police.

The Gateway service was taken down as a precaution on Friday night before reopening on Saturday evening.

A DWP spokesman said that the department is certain that the security of the gateway has not been compromised. The department has examined the stick and found that the information provides no risk of compromise.

"On the basis of an initial examination of the contents of the memory stick, it is our experts' opinion that the contents would not allow anyone to breach the very strong security safeguards protecting the web site," said the spokesman.

The memory stick loss and consequent Gateway closure have raised further questions over the planned ID cards scheme, said the Liberal Democrats.

"Why should we trust the government with our details for its database or ID cards system when they simply cannot be trusted with information? These data losses are becoming almost weekly?" Said spokesman Norman Baker.

Baker said it should have been "a basic security step" to ensure memory sticks containing sensitive information "simply don't exist".

Tory spokesman Nick Herbert said it was not good enough for ministers to sidestep blame and hold supplying firms responsible.

"The government contracts with these firms and ministers must therefore accept responsibility for ensuring that personal information will be handled properly," he said.