Sir Vince Cable has denied he is too old to be Liberal Democrat leader, after becoming the first contender to throw his hat into the ring to replace Tim Farron, who announced his resignation last week.
The 74-year-old returned to the House of Commons as MP for Twickenham in this month's General Election, having been one of the highest-profile casualties of the party's collapse in support in 2015.
Former energy secretary Sir Ed Davey and ex-health minister Norman Lamb have also indicated they are considering a bid for the leadership, but hotly-tipped East Dunbartonshire MP Jo Swinson, 37, has ruled herself out, saying she will fight for the deputy leadership instead.
Declaring his candidacy on the Lib Dem Voice website, Sir Vince said he is ready to "work with like-minded people in other parties" to ensure voters get the final say on any Brexit deal, with the option to stay in the EU if the agreement on offer is not good enough.
He described Brexit as an "iceberg" about to hit the UK economy and said the party should "warn of the dangers ahead and the need for a new course".
Despite the disappointment of the Liberal Democrats securing only 7.4% of the vote and 12 seats in this month's election, Sir Vince insisted that "the political winds are moving in our favour".
He said: "There are big opportunities ahead. The Conservatives are in disarray and in retreat. The Labour Party outperformed expectations but complacently believes that 'one more heave' will see it into office.
"But an economic policy based on offering lots of free things lacks economic credibility and will be found out. Investing in infrastructure, rather than borrowing for everyday running costs, is credible. There is a big space in British politics which I am determined that we should occupy."
Speaking on BBC Radio 5 Live, Sir Vince declined to say whether he would fight the next General Election, due in 2022 when he would be 79.
But he said he was "very much up for a contest" and did not regard his age as a barrier, pointing to William Gladstone, who became prime minister at 82 in 1892, and Bernie Sanders, who sought the Democratic presidential nomination in the US aged 74.
Sir Vince previously served as acting leader following the resignation of Sir Menzies Campbell in 2007, but declined to stand for the top job at that point, saying that an older candidate would not be electable because of "irrational prejudice about age".
If elected, he would be the party's oldest ever leader and the oldest leader of a major party since Sir Winston Churchill, who was 80 when he stepped down as Conservative leader.
Sir Vince told 5 Live's Adrian Chiles: "In four years' time the question arises of a general election coming up.
"I've then got to make a choice - do I let one of my very able younger colleagues take over, or do I do what William Gladstone did... when he was 82 (and) Winston Churchill did in his mid-seventies?
"Some of the brightest and most interesting people in British politics recently have been relatively old. You remember Bernie Sanders in America as well. I think age is a surety. I don't feel old, I feel young and energetic and I'm very much up for a contest."
Mr Farron shocked many Lib Dems by announcing days after the election that he will stand down when Parliament breaks for the summer next week.
A committed Christian who was repeatedly questioned during the election campaign over whether he saw gay sex as a sin, Mr Farron said his religion had made him a "subject of suspicion".
Contenders to replace him need nominations from at least 10% of the parliamentary party - two MPs, not including themselves - as well as at least 200 members drawn from 20 or more local parties.
After a contest stretching over the summer, the new leader will be elected by party members in a postal ballot conducted by a single transferable vote in time for the start of the Lib Dem annual conference in Bournemouth on September 16.