London: The brother-in-law of a Tory minister has donated £816,000 (Dh5.1 million) to her party since she became an MP, it emerged last night.

Andrea Leadsom, the financial services minister, said she had no idea her relative, offshore banker Peter de Putron, had given the money.

But last night a Labour MP said the payments raised questions about a possible “cash for political office” arrangement.

De Putron, a banker who lives in Guernsey, is married to Leadsom’s sister Hayley.

He has also made donations totalling £1 million to a political campaign backed by the Tories and to a right-wing think tank.

Although donations to British politicians from the Channel Islands are banned, the Leadsom payments were legally permissible because they were made through UK-registered companies.

A spokesman for Leadsom, the MP for South Northamptonshire, told the Guardian she was unaware of the donations made by a member of her own family.

The former banker was promoted earlier this year and became a member of George Osborne’s team. She was first elected in 2010.

De Putron wrote out cheques to the Conservative party totalling £200,000 in 2010, £66,600 in 2011, £129,800 in 2012, and £204,760 in 2013.

They were made via a company called Gloucester Research. Smaller sums were also made to her local constituency party.

De Putron also made smaller payments directly to Leadsom to hire staff, as well as £300,000 to the Conservative-backed “no to voting reform” campaign, and a total of £680,000 to Open Europe, a think tank which wants to see reform of the EU.

The details emerged following a leak of the identities of thousands of wealthy offshore clients who bank with a major Channel Isles private bank.

A US non-profit news organisation, the International Consortium of Investigative Journalists, has obtained records of more than 20,000 names. The leaks show many Jersey loopholes used by wealthy Britons to pass on their fortunes appear to have been perfectly legal.

Both the Tories and to a lesser extent Labour have benefited from political donations by such individuals.

Not only was the main company concerned in the donations controlled by Leadsom’s brother-in-law, but her husband, Ben, is a director.

A spokesman for the MP said: “Andrea was not aware of the size of donations made by UK companies controlled by Peter de Putron to the ... Conservative party, and has never been involved in any way.”

He added: “She has not benefited personally from these donations and does not believe they have affected her career.”

But Labour MP Tom Watson said: `This doesn’t look right.

“Most reasonable people will expect Andrea Leadsom to rid herself of the suspicion that she might be the beneficiary of a ‘cash for office’ arrangement.”