Mr Clegg retained his seat of
with an increased majority, however.
Ian Swales of the Lib Dems unexpectedly defeated Solicitor General Vera Baird in
in Cleveland, previously a Labour stronghold.
And Sarah Teather won the newly-created seat of
beating former Labour MP Dawn Butler.
'Very fluid' situation
Speaking outside the Liberal Democrats' headquarters in Westminster, Mr Clegg said it was a "source of great regret" that some of his MPs had lost their seats.
Many voters "were excited about the prospect of doing something different", he said, but had "decided to stick with what they knew best".
The UK's hung parliament had led to a "very fluid" political situation, he added, calling for Prime Minister Gordon Brown and Conservative leader David Cameron to act "in the national interest and not out of narrow party political advantage".
Former Lib Dem MP Lembit Opik was unexpectedly defeated by the Tories
Mr Clegg maintained his pre-election position that the party with the highest number of seats should have the first say in trying to form a government.
"It is now for the Conservative Party to prove that it is capable of seeking to govern in the national interest," he said.
And he called once again for the UK's electoral system to be reformed, saying it was "broken" and "simply doesn't reflect the hopes and aspirations of the British people".
Earlier, when his own result was declared, Mr Clegg said he would be "guided by the values and the principles on which we fought this election".
These were "fairness in our society; responsibility in providing stability and growth to an economy at a time particularly of growing uncertainty, as we have seen in recent hours and days in the economy in the world around us; and real change to the way we do politics."
Liberal Democrat MPs and peers will hold a private meeting on Saturday to begin considering how their party might work with Labour or the Conservatives.
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