Liberal Democrats were “perfectly reasonable” to block boundary changes in return for the Tories' failure to meet other parts of the coalition deal, Nick Clegg said.
The Deputy Prime Minister hit back at Conservative critics after his peers sided with Labour to inflict a bruising defeat on the Government last night.
They secured an amendment delaying the implementation of the constituency shake-up - thought by experts to be worth up to 20 extra seats for the Tories - until after the 2015 general election.
Six of the seven Lib Dem frontbenchers in the upper chamber joined the revolt - the first time in this Parliament that ministers in either House have voted against the Government.
Downing Street said Prime Minister David Cameron would seek to overturn the amendment in the Commons, but without an overall Tory majority the parliamentary arithmetic is against him.
Mr Clegg made clear over the summer that the Lib Dems would seek to delay the plans after he was forced to abandon plans to reform the House of Lords in the face of Tory opposition.
In the aftermath of the vote, he was accused by Conservative peers of "cheating" and "a great political sulk".
But Mr Clegg told BBC Radio 4's Today: "You will remember, of course, back in the referendum on the Alternative Vote system the highly-regrettable personalised attack by the Conservatives then.
"You will remember, of course, the House of Lords debate where the Conservative Party decided not to proceed with reform even though it was in their own manifesto and the Coalition Agreement.
"I have been very open about the fact that a coalition, by definition, is a package deal and when one side of that package, that deal, does not honour their side of the agreement then I think it's perfectly reasonable for the other side (to look at other parts of it).
"We are not voting them down; what we are saying is there is going to be a delay of five years.
"We are leaving the boundary changes on the statute book but we are saying that we should miss a beat and do it in the next parliament not this one."