The Greens have hit back at calls by a key Corbyn ally for a formal merger between the Labour Party and the Green Party.

Jon Lansman, the founder of Momentum – the Corbyn-backing campaign group – recently raised the prospect of taking a ‘progressive alliance’ to the next level through the Greens becoming a semi-formal wing of the Labour Party – in a similar relationship to the Co-Operative Party, which does not run candidates against Labour.

Speaking at a Labour conference fringe meeting in Liverpool on Tuesday, Lansman said: ‘Why shouldn’t the Green party have the same relationship with the Labour party that the Co-op party has with the Labour Party?,’ according to politics.co.uk.

Lansman said under his proposed model, Greens would be able to join Labour with equal voting rights, ‘including the very important one of selecting candidates’.

However, a senior source ruled out the prospect of any merger between Labour and the Greens: ‘We’re not going to become a party within the Labour party. [We’ll stay] separate parties, working together when possible/useful.’

Caroline Lucas, co-leader of the Green Party, told the left-wing blogging site ‘Left Foot Forward’: ‘

‘While I have great respect for the traditions of the Labour Party, and agree with the leadership on many things, I believe both in the distinctiveness of Green policy and in the merits of a multiparty democracy. That’s why my Party will continue to make our united voice heard loudly and clearly, on issues such as trident replacement, stopping Hinkley power station and democratizing the post-referendum process, but we’ll also look to work across party lines wherever there is common ground.’

However, she added:

‘Since no one single party has a monopoly on wisdom, and the chances of a Labour majority are vanishingly small, we owe it to the public to explore whether our separate parties can work together to bring about a progressive Government at the next election.’ She said backing proportional representation would be a condition of the Greens engaging in any progressive alliance.’

Another senior Green Party figure responded to Lansman’s merger plans, telling Left Foot Forward:

‘There’s room for doing something differently, but the idea of being a wing of the Labour Party is just patronising.’

A progressive alliance – including a formal pact between Labour and the Greens – was a key plank of Caroline Lucas MP and Jonathan Bartley’s leadership campaign this summer, with the two securing 87 per cent of the vote.

However, the response from Lucas and other senior figures suggests anything more serious than standing down in selected seats on the condition of Labour backing PR is off the cards – at least for now.

This article originally appeared on Left Foot Forward.