De Rothschild — known as Lynn Forester before she married the banker Sir Evelyn de Rothschild in 2000 — was one of the Democrats most successful fundraisers. She also paid for and organised all President Bill Clinton’s third way conferences, having made more than £100m from the sale of two communications companies she started.

Since her marriage, de Rothschild, 48, has been based in London. Her 71-year-old husband is head of the merchant bank NM Rothschild and his family has a fortune of £500m.

Recently she hosted a party for her friend Hillary Clinton. She has also become close to Tony Blair and Gordon Brown. Peter Mandelson is said to be “smitten”. Many Labour stalwarts are likely to be worried at the prospect of the party consorting with grandees such as the de Rothschilds.

But with Labour short of funds to fight the next election — membership and donations from unions are both down — de Rothschild’s intervention could be crucial.

“Whatever Labour wants, I would be happy to help in any way I can,” she says in an interview in today’s Sunday Times News Review.

“Fundraise? I would. I think a lot of this government.”

De Rothschild, who spent her wedding night in the White House as a guest of the Clintons, defended holding such wealth while espousing centre-left opinions: “It is not about being a limousine liberal. I work hard, not only for myself but for others, and I would fight to the death to preserve our way of life.”

Explore UK News

• Crime News

• Education News

• Health News

• Science News

• Scotland News

Times Recommends

• Scots may get more tax-raising powers
• Why team games may make your children fat
• Ivy League targets Britain’s top students