Energy Secretary Ed Davey said the Tories and Liberal Democrats were parties with different values and histories.
But he defended the coalition in the wake of this week's Conservative rebellion on Lords reform - and insisted the plans were not dead.
He told the Sky News Murnaghan programme:
People are forgetting that we had a historic vote in the Commons just recently when a huge majority voted in favour of the principle of a democratically elected House of Lords.
That has not happened before. I also believe it is part of the Coalition Agreement and the Conservative Party will want to honour their agreement and I'm delighted the Prime Minister said he's going to have another go.
Coalition differences set aside as multi-billion pound rail improvement is announced
David Cameron has issued an appeal to warring Tories and Liberal Democrats to unite behind the coalition.