Under pressure Clegg defiant after Lib Dem election losses
Nick Clegg has rejected calls for him to stand down as leader of the Liberal Democrats after the party's worst European election result for 25 years.
Lib Dem MP John Pugh said Vince Cable should replace Mr Clegg after the party lost all but one of its 12 MEPs.
The MP told the BBC it was "ludicrous" to carry on as usual.
But Mr Clegg said he was proud of having taken on UKIP and "stood up for the values that we believe in", even though, he said, "it didn't work".
And he got support from Mr Cable, the business secretary, who said: "There is no leadership issue... now is not the time for infighting and introspection. The party must hold its nerve."
The Lib Dems got 6.9% of votes, down from 13.7% in 2009, leaving them in fifth place behind the Green Party, as they lost seats in every region apart from the South East of England.
Mr Clegg told the BBC: "There are some individuals who say they want a change of leadership, a change of strategy, or who want to pull out of the coalition altogether. Of course it is right to have searching questions in the wake of such a bad set of election results.
"The easiest thing in politics, and sometimes in life, when the going gets really, really tough, is just to walk away, to wash your hands of it.
"I'm not going to do that and my party's not going to do that.
"The vast majority of Liberal Democrats do not believe that we should lose our nerve and walk away just now."
The election results had been a "huge setback", he said, but his party was "the most united, resilient, toughest party in British politics" and he was "immensely proud" of leading it.
"Uniquely in British politics, the Liberal Democrats decided to take on UKIP and argue for the things we believe in: a generous-hearted, open-minded, internationalist Britain," he said.
"It didn't work but it is right that we stood up for the values that we believe in."
He also defended the decision to enter coalition with the Conservatives, arguing that the Lib Dems had enabled the UK economy to recover while bringing about policies that were fair to people on low incomes.
Lib Dems expected to fare badly in the elections but party president Tim Farron has said its performance - coupled with the loss of 250 council seats in the local elections - was "staggeringly disappointing".
Mr Farron, Sir Menzies and Lord Ashdown - another former leader who is running the party's general election campaign - have defended Mr Clegg's leadership and appealed for party unity.
But Mr Pugh, the MP for Southport, said the party was underestimating the difficulties it was in and there was an "overwhelming" case for Mr Clegg's future to be discussed.
"We have just lost 72% of the council seats we were defending and 91% of the Euro seats," he said.
"The vast majority of the UK this morning is without Lib Dem representation at any level. If that does not prompt a serious, sharp review focussed view both of strategy and leadership, then whatever will!
"Orders just to press on regardless are genuinely of Somme-like insanity."
Mr Pugh said a "section of the electorate" was not listening to Mr Clegg and that his "personal preference" was for a "Cable succession".
Any transition to a new leader must take place "without aggravation or discord", he told the BBC News Channel, and if the party decided to stick with Mr Clegg, he said he would "knuckle" down and accept it.
Asked whether other MPs shared his views, he said. "All MPs see the problem. What they don't all agree on is the solution."
A third general election candidate, Helen Flynn, has called for Mr Clegg to stand down amid mumblings in the party which the BBC expects to increase during the day.
Martin Tod, a member of the Liberal Democrats' federal executive, claimed voters were "not prepared" to listen to Mr Clegg and said his party's response to the election reversals had been "complacent".
Former MP Sandra Gidley, one of about 250 people to have signed an online letter demanding a change of leader, said Mr Clegg was "associated with the broken promises of the coalition".
She told the BBC's Today programme that a new leader would be able to better articulate the "positive difference" the party had made by working with the Conservatives.
But Treasury Chief Secretary Danny Alexander, who has been touted as a future leader himself, insisted Mr Clegg was "by far the best spokesman" for the Lib Dems.
Sir Menzies said the Lib Dems had had to fight the election in a "febrile" eurosceptic climate.
"There's no doubt in my mind that Nick Clegg is the person with the courage and the resilience to take the party through to and during, and indeed after, the next general election."
Catherine Bearder, the only Liberal Democrat MEP to be elected so far, said Mr Clegg had been right to go out and campaign on a positive EU platform.
"It's been very difficult," she told Sky News. "We fought a very good, positive campaign on our issues of being in the European Union and standing up for Britain in the European Union."
She denied Mr Clegg or the EU as a whole had proved unpopular on the doorstep, but added: "People don't understand how the European Union works and they don't think it is important to their daily lives."
Some MPs have expressed reservations about the leadership of the party but none have yet called for Mr Clegg - who took over in 2007 - to stand down.
Among MEPs to lose their seats include veterans Sir Graham Watson, Andrew Duff and Bill Newton Dunn as well as Edward McMillan-Scott, an ex-Tory who was the only British vice-president of the European Parliament.