Deputy Prime Minister and Sheffield Hallam MP Nick Clegg was confronted by a former Liberal Democrat councillor who told him he had torn up his party membership card because he was ashamed of what they were doing in Government.
The clash came as the Liberal Democrat leader held the first of a weekly Call Clegg phone-in on London's LBC 97.3 radio.
Mr Clegg has said he is doing the programme, with presenter Nick Ferrari, because he feels politicians do not hear enough from voters directly, and one caller told him his decision to take part was "very commendable".
But caller John, told him:
He challenged Mr Clegg to explain how he could reconcile the party's principles with "this Government's attacks on the poorest in society".
Mr Clegg asked John to give the party credit for measures like raising the income tax threshold and introducing a pupil premium for children from disadvantaged backgrounds.
Another caller, a Sheffield University student called Lauren, dismissed measures like the pupil premium as "tokenistic" and accused the Government of discouraging young people from gaining qualifications by abolishing the educational maintenance allowance and increasing tuition fees.
The Deputy Prime Minister repeated his apology for committing the Lib Dems not to raise tuition fees when they were not in a position to deliver on the promise, and he admitted the party's recent eighth position in the Rotherham by-election was a "woeful result".
But he said it was always going to be "monumentally controversial" for them to enter coalition with any other party, and said voters were willing to give their support when they had a chance to explain their actions.