Politicians tell "brazen lies", senior Lib Dem Sir Malcolm Bruce has claimed as he defended the actions of ex-Scottish Secretary Alistair Carmichael.
Mr Carmichael is facing calls to resign after admitting he backed the leaking of a memo during the election campaign incorrectly suggesting Nicola Sturgeon wanted David Cameron as prime minister.
The MP for Orkney and Shetland said previously he had not been aware of it.
Sir Malcolm said the MP had been wrong but lying was common in public life.
The SNP have called on Mr Carmichael - the only remaining Lib Dem MP in Scotland - to consider his position after an official Cabinet Office inquiry found he approved the leak of an official memo by his special adviser to a newspaper during the campaign.
The document, written by a civil servant in the Scotland Office, claimed the Scottish First Minister told the French Ambassador to the UK that she would prefer Mr Cameron as prime minister rather than Ed Miliband - comments Ms Sturgeon has always insisted she never made.
At the time, Mr Carmichael said the first he had heard of the memo was when he was contacted by a journalist.
He has since acknowledged that while he had not seen the document before it was published, he was aware of its content and agreed that it should be made public.
The parliamentary standards commissioner has said she has received a number of complaints about Mr Carmichael's conduct and is considering whether they fall within her remit.
The BBC's Tim Reid said Mr Carmichael was not an MP at the time of the episode - because parliament had broken up for the general election - but he was campaigning to retain his seat and remained a cabinet minister.
A member of the public has also complained to the police about Mr Carmichael's conduct, our correspondent added.
Sir Malcolm said Mr Carmichael had faced up to the consequences of his actions, having apologised and foregone the severance pay he was entitled to after losing his Cabinet position.
But he told the BBC that it was "perfectly reasonable" for him to remain as a "first-class" MP for Orkney and Shetland.
"Alistair has recognised that he has made a mistake," he told Radio 4's Today programme. "People are entitled to make mistakes, learn from them and move on."
Sir Malcolm, who was MP for 30 years until retiring at the election, said Scotland was a "divided and bruised" country after the election and that Mr Carmichael, as one of only three non-SNP MPs elected to Westminster, had a key role to play in representing his constituents and holding both the UK and Scottish governments to account.
The SNP, he said, were "judging people by standards that they do not apply to themselves" and if Mr Carmichael quit "what we will have seen is the SNP bully a very good MP out of office for a mistake he has acknowledged and apologised for".
"The SNP clearly want to extinguish all opposition in Scotland. That is their objective and they will stop at nothing to do it."
Asked whether it would be acceptable for an MP who had not told the truth to remain in office, he replied: "I'm acknowledging that if (Mr Carmichael) has said 'I didn't know about something I did know in the heated atmosphere of an election campaign' that was part of the mistake, which he has apologised for."
"My point is if you are suggesting that every MP who has never quite told the truth or indeed told a brazen lie - including ministers, including Cabinet ministers, including prime ministers - we would clear out the House of Commons very fast, I would suggest.
Asked if lying was widespread in public life, he said: "No, well, yes. I think the answer is that lots of people have told lies and you know that to be perfectly true....
He added: "We should, of course, hold people to account and if people lie they should take some consequences but Alistair has taken consequences."
The SNP said the comments amounted to an "increasingly desperate attempt to defend the indefensible".
"Being an MP or MSP is a huge privilege for anyone elected to serve - and untruthfulness can never be simply brushed aside in the way that Sir Malcolm suggests it should," said MP Pete Wishart.
"The Lib Dems' defence of Mr Carmichael gets more ludicrous by the day, and all Sir Malcolm has succeeded in doing is to keep the focus on his colleague."
The Cabinet Office said the cost of its investigation had been "minimal" and said there were no plans for a further investigation into whether Mr Carmichael had breached the ministerial code.
Labour MP John Mann said the row illustrated the need for a stronger system of voter recall for politicians accused of misconduct. "There are plenty of people who avoid answering a question but that is not the same as lying," he said.
Under a law championed by the Lib Dems in the last Parliament, an MP's seat becomes vacant if they are suspended from the Commons for at least 10 days and a 10% of their constituents subsequently sign a petition calling for a by-election.
There has also been criticism from one prominent Lib Dem activist. "It is a rubbish defence/excuse and not one a party reduced from 57 MPs to just 8 should be making," tweeted Stephen Tall, former co-editor of the Lib Dem Voice website.
The Scottish Liberal Democrats have said that Mr Carmichael, who held off a strong challenge from the SNP to regain his seat by 817 votes, will not face any disciplinary action.