Adrian Ramsay, the former co-leader of the Greens, has urged his party’s councillors to reject the newly adopted “Zionism is racism” motion if it will help them stay in power in local government, in a fresh sign of internal dissent over the policy.

Ramsay, one of the Greens’ five MPs, said he was pleased that a number of Green council groups had already condemned the policy, which was adopted at the party’s conference and also calls for a single Palestinian state in place of Israel.

Last week, Labour ordered its local parties who share power on councils with Greens to terminate the deals if the local Greens did not disown the policy motion.

In a statement to the Guardian, Ramsay, who co-led the Greens in England and Wales for four years until Zack Polanski took over last year, said that while he understood why Green groups might not want to be “bullied” into action by Labour, it was important for them to be clear about the motion and to maintain coalitions where possible.

Ramsay expressed his opposition to the motion before the vote at the party conference earlier this month but had subsequently not commented.

Such a public call to Green councillors places him at odds with Polanski, who has said he will not seek to overturn the motion, and with the official party line, which stated that the Greens will “not take lectures” from a Labour government that supplies arms to Israel.

A series of Green council groups who share power with Labour have already rejected the motion, including Lewes, Warwick, Rother and Havant. Among other groups to have disowned the policy are the Greens in Southwark, who did so to maintain a coalition with the Liberal Democrats.

Ramsay said such groups “have been brave in speaking out about such a contentious motion”.

He said: “They have supported the Green party’s strong position of calling out the ethnic cleansing and war crimes in Gaza and how this must be combined with upholding the right of both Palestinians and Israelis to statehood and self-determination. Calling out a genocide is more important than debating definitions of Zionism.”

Ramsay said his advice to other groups still deciding was to make their opposition to the motion clear if that was what they believed, saying it would “reassure a lot of people in your communities, and it will enable you to continue making a real difference for your residents”.

He said Labour’s ultimatum about the policy was “entirely predictable” and it was understandable that Green councillors “don’t want to be bullied into making a statement by a diktat from the national Labour party which has been served on local Labour groups”.

It would, however, “be incredibly sad to see joint council administrations fold because of this – especially as the alternative will often be a rightwing coalition that could see services put at risk,” he argued.

Green-run or jointly run councils were making a real difference, Ramsay said. “We can’t let this be undermined by a party conference motion which is a distraction from this work, and which I am confident is not supported by most party members.”

Speaking to the BBC on Sunday, Polanski defended the motion and said the policy would stand for at least two years, given party rules, but he wanted to amend it to remove the call for a single Palestinian state.

He said: “I’m not going to try and overturn it. At the first available opportunity, I do want to amend it.”