Conservative former MP Michael Portillo described the moment he lost his seat in the 1997 General Election as a “great relief”.

Mr Portillo gave a talk at Dauntsey’s School on Friday.

More than 800 people packed the Memorial Hall to hear him speak about the most embarrassing experience of his political life when he delivered the latest Mercers’ lecture.

He told the audience: “It was actually a great relief to me. I would certainly have been in the running for party leader and there was no way we were going to be re-elected for the next five, and most likely, ten years.”

The defeat led to a new career as a broadcaster and he is now almost as well known for his TV series on railway journeys as he is as a former Defence Secretary and “former future Prime Minister”.

He did reveal interesting political angles. He was the only Conservative politician to advise Margaret Thatcher to her face to fight for the leadership after her cabinet had urged her to resign.

He was asked his opinion of Mayor of London Boris Johnson’s prospects of becoming Prime Minister.

Mr Portillo said: “David Cameron is a serious politician with serious policies. I am not convinced that Boris is serious.”