Ed Miliband has revealed he held “surreptitious conversations” with Sir Vince Cable while he leader of the Opposition.

Miliband today also gave his support to electoral reform as a way of “reconstructing our faith in politics”, following an anti-politics mood among voters that led to June’s Brexit outcome.

The talks between Miliband and Cable, which occurred during the last parliament when the latter was Lib Dem Business Secretary, were highlighted when they took part in a discussion at the New Economics Foundation conference.

Miliband admitted the pair had taken part in “various surreptitious conversation over the last few years”, while Cable – also a former Labour councillor – said that progressives “should try and break through the traditional tribal divisions”.

The Doncaster North MP argued that major reforms of the political system are necessary in order to regain the trust of voters.

“What was the Brexit coalition? What was the uniting factor of the Brexit coalition? Part of it was an anti-politics identification,” Miliband said, adding that supporting “political reform is becoming a litmus test of whether you are serious about solving the issues that mainstream politics faces”.

“Political reform is the essential part of reconstructing our democracy and reconstructing our faith in politics. Electoral reform, but also beyond that, where power lies”, he said.

While he admitted that voters had never demanded “we need the additional member system” during doorstep conversations, he said it is only through major reforms that people will start to feel part of politics once again. Miliband said that the two main arguments the left need to make are for “a radical assault on economic inequality and big political reform.”

“We have to offer that as an alternative to what Theresa May is offering,” he said, arguing that the British public have not shifted to the right, calling the current situation a “paradox”: “On some issues the country has moved the left, on some issues the country has moved to the right.”

But Miliband also warned that for Labour to “surmount” the “politics of identity” and “find a new coalition” of support to take it into government, it needs to ensure that “the scale of cultural change in the party is going to match the increase in membership”. He made a case for the party more boldly embracing community organising, and namechecked Arnie Graf, who has been influential on the subject.