Michael Ancram, the former deputy leader, Richard Spring, the party vice-chairman, and the Shadow ministers Caroline Spelman and Mark Simmonds flew across four continents from 2002 to 2004.

Mr Ancram’s flights and hospitality amounted to £33,000 in gifts from an aviation company based in the Atlantic tax haven of Bermuda. The MP has told the Electoral Commission that the business is owned by Lord Ashcroft, the former party treasurer.

Although the law insists that donations must be declared to the commission within 30 days, the MPs have been spared having to repay the money. The commission also decided against calling in detectives after accepting that none of the four had deliberately concealed the benefits.

The New Politics Network, which campaigns for party funding reform, emphasised the importance of transparency and expressed concern that MPs had failed to understand the system. Parties are banned from taking overseas donations but individual politicians may accept travel expenses from abroad for their work.

The politicians took flights to the Caribbean, the Middle East, South Africa and Eastern Europe. Accommodation was sometimes included. They declared the travel on the Commons Register of Members’ Interests, stating their destinations and describing the donor as Flying Lion Ltd.

But they failed in their obligation to tell the commission, which requires more extensive details, such as the value of gifts and the addresses of donors. Only after The Times launched its inquiries did the MPs make their disclosures.

Mr Ancram’s bemusement rings through in a letter to Sam Younger, the Electoral Commission chairman, obtained by The Times under the Freedom of Information Act: “Dear Sam, I remain somewhat confused about the position of Shadow Foreign Secretary, Shadow DFID and Shadow Defence Secretary and their teams for whom sponsored foreign travel is effectively the only way that they can carry out their duties as members of HM Opposition. From our conversation I believe that we both see this as somewhat of a grey area and, although it no longer affects me, I believe it is one which would benefit from clarification.

“Flying Lion Ltd is owned by Lord Ashcroft of Chichester KC MG, formerly treasurer of the Conservative Party and now deputy chairman and a donor to the party of long standing.”

Andrew Mitchell, currently the Shadow International Development Secretary, is the only MP who declared to the commission his gifts of £12,000 travel to Africa from the offshore company before The Times began investigating. He seems to have known little of his sponsor, e-mailing the commission: “Somewhat akin to The Da Vinci Code this one, but I have finally tracked down the address for Flying Lions.”

A commission spokeswoman said: “In respect of the offences available under the Political Parties, Elections and Referendums Act for late reporting of donations, we take the view that there was no intent to conceal the donations, as they were reported on the Register of Members’ Interests. It therefore wouldn’t be appropriate for the commission to refer the matter to the police.”

A Conservative Party spokesman said: “These MPs acted in good faith and all registered these important trips with the Commons authorities. They were given to understand that they had fulfilled all the reporting requirements. When it was later explained [that] they needed to register the trips with the Electoral Commission as well, they took all necessary steps to do so. As the Electoral Commission itself points out, there was no intention to conceal any of the facts.”

HOW THE MONEY WAS SPENT

• Michael Ancram, as Shadow Foreign Secretary, visited South Africa, Zimbabwe, Malawi, Sudan, Kenya, Kabul, Baghdad, Estonia, Latvia, Lithuania, Poland, Afghanistan, Georgia, Turkey, Cuba, Turks and Caicos Islands, St Kitts and Nevis, Grand Cayman, Egypt and Israel

  Value £33,000

• Caroline Spelman, then Shadow International Development Secretary, went to Afghanistan, Kuwait, eastern and southern Africa

  Value £11,000

• Richard Spring, as foreign affairs spokesman, visited South Africa, Zimbabawe and Malawi.

  Value £8,000

• Mark Simmonds, as foreign affairs spokesman, flew to Cuba, Turks and Caicos, St Kitts and Nevis and Grand Cayman

  Value £3,600

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