Home Secretary Jacqui Smith is facing a Commons summons to explain the latest Government security lapse after another batch of secret papers were left on a train.

The documents, covering global terrorist funding, drugs trafficking and money laundering, were handed in to The Independent on Sunday after being found last Wednesday on a train heading for London's Waterloo Station.

Their discovery coincided with a similar incident when secret Joint Intelligence Committee (JIC) assessments on Iraq and al Qaeda were passed to the BBC after they also were left on a train.

Although neither incident involved the Home Office, Keith Vaz, the chairman of the Commons Home Affairs Committee, said they would be calling Ms Smith to explain the implications of the losses for the fight against terrorism.

"Only on Thursday the Government told Parliament that it had established an inquiry into the confidential documents left by an official on a train and handed to the BBC. This latest revelation gives us serious cause for concern," he said.

"We need an explanation from the Home Secretary whether all these breaches of security affect our fight against terrorism."

Mr Vaz said: "Until the inquiry has been concluded and we are told how these extraordinary events occurred, no official, no matter how senior, should be allowed to take classified or confidential documents outside their offices for whatever reason."

The latest documents to go missing related to a week-long conference of the 34-nation Financial Action Task Force, beginning on Monday at London's QE2 Centre opposite the Houses of Parliament.

They were said to include details of how trade and banking systems could be manipulated to finance illicit weapons of mass destruction in Iran and the potential fraud of commercial websites and international internet payment systems.

They also included speaking notes for a senior official at a reception to be held at 11 Downing Street, Chancellor Alistair Darling's official residence.

Although they do not appear to have been as sensitive as the JIC papers - and were said to include publicly available material - the Government said that it was taking the loss seriously.

A Treasury spokesman said: "We are extremely concerned about what has happened and we will be taking steps to ensure that it doesn't happen in the future."

Foreign Secretary David Miliband said all such reported breaches of security were taken extremely seriously.

"These sorts of lapses are completely inexcusable. I know that this will be taken with the utmost seriousness and will be followed up to ensure that there isn't a further threat to the national interest," he said.

The Treasury refused to say whether the individual responsible had been identified.

The Cabinet Office said that the Cabinet Secretary Sir Gus O'Donnell was writing to all permanent secretaries across Whitehall to remind them of the importance of ensuring that officials were aware of the need to handle information with care.

For the Tories, shadow security minister Baroness Neville-Jones said the Government must "get a grip" on the issue of data protection.

"This is another incidence of the failure of the Government to safeguard sensitive information and yet another example of a lapse in discipline," she said.

"In this case had the content been released the potential consequences could have included prejudicing the UK's position in international meetings - the Government cannot allow this to continue."

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