Mr Clegg said the petitions were needed for cases like that of Derek Conway, who was able to stay as an MP despite being suspended from Parliament and kicked out of the Conservative Party.
"It seems to me, at least in that situation, where someone has been proven to do something seriously wrong, that people should be able to sack their MP."
Mr Clegg said the revelations about MP expenses were just "the tip of the iceberg" of things relating to money and politics that had to be sorted out.
He said Labour were bankrolled by a few trade union chiefs and the Conservatives "in large part by people who don't even pay full taxes in this country", and "we (the Lib Dems) have our own problem with one major dodgy donor".
The Lib Dem donor he referred to was Michael Brown, a bogus international bonds dealer who is on the run, who became the biggest donor to the party ahead of the 2005 general election.
Since then he has been convicted in his absence of stealing more than £30m from people including ex-Manchester United chairman Martin Edwards.
Some of those who lost money invested with Mr Brown want the Liberal Democrats to repay the money.
In 2006 the Electoral Commission said they believed that at the time, ahead of the 2005 election, it was "reasonable" for the party to regard his donation as "permissible".
When MPs knowingly exploited the expenses system for profit, they knew they were doing that at the time
Nick Clegg Lib Dem leader
But the BBC understands that the Electoral Commission has now resumed its inquiry into the permissibility of those donations and could require the party to forfeit the donations.
Asked how he could "morally justify" keeping the money , Mr Clegg said: "We took every single step to confirm whether he was eligible... Later we discovered the guy was a crook.
"If I'd have known then what I know now, of course we wouldn't have accepted a single penny but I don't think we've got £2.4m lying around to give back to anyone."
Mr Clegg denied there was a similarity between his argument and the argument made by MPs refusing to pay back expense claims because they followed "the rules".
He said: "When MPs knowingly exploited the expenses system for profit, they knew they were doing that at the time.
"What we did was we took money from a donor, took every reasonable check, this has been recognised by the Electoral Commission that we took that money in good faith... you're casting aspersions, very unfairly on the checks that we took at the time in to Michael Brown."
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