As late as March, however, Mrs Clinton was openly comparing herself to Lady Thatcher. "If people have doubts about a woman, they should look at Margaret Thatcher or Angela Merkel or other women who have been leaders of important countries - Golda Meir, Indira Gandhi, my late friend Benazir Bhutto and so many others," she said in Toledo, Ohio in March.

The trumpeting of Lady Thatcher's qualities by Mr Penn, who has advised Gordon Brown and Tony Blair and is close to other senior Labour party figures, will confirm the suspicions of liberal Democrats that he and Mrs Clinton were out of step with the party's progressive wing and grassroots.

Joe Trippi, a veteran Democratic strategist who was a top adviser to the rival John Edwards campaign, said: "It's hard to run as Margaret Thatcher and be change. That was Hillary Clinton's whole problem.

"As a role model, it just goes against the grain and to try to map your strategy around that personality is not dealing with reality, both ideologically and in terms of the different era. Thatcher had the Falklands, George Bush had Iraq - we've got the exact opposite of the Thatcher situation."