Ed Miliband refused to share a referendum platform with Nick Clegg because the Liberal Democrat leader "shocked" Britain, he has claimed.
Senior Lib Dems including Vince Cable, Paddy Ashdown and Charles Kennedy have all appeared alongside Mr Miliband during Yes to Fairer Votes campaign events but Labour strategists have decided the leader of the opposition should not share a platform with the deputy prime minister.
"The truth is, a year ago we all remember Cleggmania - people thought he was the poster child for new politics," Mr Miliband told the Today programme.
"I'm afraid he has essentially broken many of his promises in a way that looks like the old politics."
Yesterday Mr Clegg suggested he had been naive to hope the referendum campaign would not have quickly disintegrated into party politics.
Mr Miliband insisted he wanted to keep the deputy prime minister at arm's length not because of partisanship but because he wanted to win the referendum, which he called "a once-in-a-generation chance for people to change their politics in this country".
"I think people have been shocked by what Nick Clegg did, which is to pose as somebody of the centre-left, and then go in with a Conservative-led government that is pursuing things that it doesn't have a mandate for - on the NHS, on tuition fees and on the deficit," he added.
"All of those things are the opposite of what Nick Clegg said.
"I hope people vote Labour on those issues, because I think they do need to send a message to this government without a mandate, but I hope they don't use the referendum to kick Nick Clegg."
Both the 'yes' and 'no' campaign are engaging in the final full day of campaigning before polling stations open tomorrow at 07:00 BST.