Jo Swinson was accused of being a “Tory in disguise” by a member of the audience at a TV election debate.
An unidentified woman in the audience asked her: “Why doesn’t Jo Swinson show her true colours? They’re blue. You’re a Tory in disguise, state what you are.
“You dare to try and raise taxes on lower earners when the country is in austerity. How dare you.”
Ms Swinson responded by saying her party was being “honest” about how it would end austerity and invest in public services.
“If you look at the independent Institute for Fiscal Studies, they have looked at the Labour plan and they say they are not credible,” she added.
The Lib Dem leader was also repeatedly criticised for supporting welfare cuts while she was a member of the coalition government between 2010 and 2015.
Shadow education secretary Angela Rayner, who represented Labour, told her: “You voted for the bedroom tax, you voted for austerity, you voted for tuition fees. You did that nine years ago – apologise for tuition fees.”
Ms Swinson responded by accusing Labour of ”making a list of promises that you cannot deliver”.
The debate on Sunday night was shunned by the Conservatives and Brexit Party, who were represented by two empty podiums alongside the Lib Dems, Labour, SNP, Greens and Plaid Cymru politicians.
Instead presenter Cathy Newman was forced to read out the Tory responses to some of the questions.
Ms Swinson said: “To be honest I think they should have turned up if they wanted to be represented – just like Boris Johnson couldn’t be bothered to turn up to the Channel 4 climate change debate.
“It tells you exactly what the Tories think about the importance of the environment in this election.”
Last month’s climate change debate saw the absent Boris Johnson and Nigel Farage being replaced with melting ice sculptures.
Additional reporting by Press Association