The wife of a former Russian minister is to pay the Conservatives £160,000 to play a game of tennis with Prime Minister David Cameron and London Mayor Boris Johnson.
Lubov Chernukhin, whose husband served under Vladimir Putin, netted the prize at a fundraising auction held during the party's summer ball in London.
Mrs Chernukhin is a longstanding Conservative Party donor.
The party has declined to confirm who attended Wednesday's social event.
Items reportedly auctioned off at the Hurlingham Club, in west London, include a £45,000 bottle of champagne signed by the late prime minister Lady Thatcher and a £15,000 jar of honey made by Foreign Office minister and keen apiarist Hugo Swire.
'£12,000 a table'
The Bureau of Investigative Journalism, which first reported the story, said David Cameron, Theresa May, Philip Hammond and Boris Johnson were among the senior Conservatives who were guests at tables hosted by prominent businessmen and donors costing up to £1,000 per head.
Labour has called for details of the guest list to be released, saying it raises questions about the Conservatives' links with wealthy donors.
The Guardian said Wednesday's auction alone raised £500,000 for the party's general election war chest.
The prize lot at the event was a tennis match with the prime minister and mayor of London, both keen exponents of the game.
Law firm Carter Ruck confirmed the successful bidder was Lubov Chernukhin, whose husband Vladimir was deputy finance minister under Mr Putin between 2000 and 2002.
"Mrs Chernukhin, who is a Conservative Party member and supporter, attended the Hurlingham Club event with her husband, Vladimir Chernukhin," it said in a statement.
"Mrs Chernukhin bid on the lot referred to... Mrs Chernukhin's bid was successful."
Lubov Chernukhin, whose husband has built a number of business interests in the UK, is a British citizen.
In 2012, a £10,000 donation she gave to the Conservatives was deemed "impermissible" because, although she was eligible to vote, she was not actually on the electoral register at the time.
'Tangible or intangible'
Since then, she has given £5,500 in three separate donations.
All single donations in excess of £7,500 must be reported and parties are required to put a price on auction prizes, by way of a "honest assessment" to determine whether they should be declared.
In its guidance, the Electoral Commission says prizes should be regarded as either "tangible items" or "intangible benefits" - acknowledging that the value of the latter, such as a "picture signed by a prominent political figure may be harder to determine".
The Independent said New Century Media, which is also reported to have links to the Russian government, was among the companies paying for a table on Wednesday.
The corporate communications firm, set up by the former Ulster Unionist MP David Burnside, donated £85,000 to the party in 2009-2010, representing nearly a third of its total £267,000 profit for the year.
The company also gave a £6,000 donation in June 2010, shortly after David Cameron entered Downing Street, but has not donated any money since then.
On its website, the firm says it has "particularly strong credentials" in Russia and the rest of the former Soviet Union, "providing strategic advice to governments, major companies and high profile individuals doing business in or with Russia and other Central and Eastern European countries".
Its clients include the Firtash Foundation, set up by the Ukrainian billionaire Dmitry Firtash, and the Moscow International Finance Centre.
Foreign nationals and governments are banned from donating money to British political parties, but there is nothing to stop lobbying firms working on their behalf giving donations - as long as they are registered in the UK.
The firm told the Independent that all donations were correctly reported to the Electoral Commission.