A deal offered to striking bin workers in Birmingham has been watered down, their union claims.

Unite has called for further negotiations with the city council after a “ball park” proposal discussed at talks with conciliation service Acas had been revised “by government commissioners and the council leader”.

An all-out strike in the city is now in its third month, after staff walked out on 11 March over plans to downgrade some roles, which the union says could cost workers £8,000 a year.

Birmingham City Council said it had made an updated, fair and reasonable offer to the union that it was asking to be shared with members.

Talks between the Labour-run council and Unite have been taking place with the conciliation service since the start of May, after previous negotiations to resolve the strike ended without a solution.

The union’s latest statement accuses the authority of missing deadlines on the proposals which had been tabled on Friday evening.

“After weeks and weeks of saying one thing in public and another to workers, the government commissioners finally allow a proposal to be put on the table,” said Unite’s General Secretary Sharon Graham.

She said the offer had been watered down by the council leader and government commissioners “who were not in the negotiating room”.

The council said it was hopeful talks between the two parties would continue next week, “as we remain committed to reach a negotiated settlement to end this dispute”.

Ms Graham said the offer would be discussed with reps over the weekend and a detailed response would be issued ahead of a reconvened Acas meeting.

“The actual decision makers now need to be in the room at the further ACAS talks,” she said.

A court order preventing striking workers from delaying bin lorries leaving depots in the city will continue indefinitely, it was confirmed on Thursday.

The union said it was preparing to challenge the injunction, but said it agreed to abide by the law on picketing.

On 23 May, when the injunction was granted, the city council said disruption at depots had led to a backlog of up to 12,800 tonnes of waste.

Police recently scaled down their presence on picket lines, where they had been helping to ensure bin trucks could get out of the depots, to prevent waste piling up on city streets.

The West Midlands force withdrew after stating the issues did “not meet the threshold” to impose powers under Section 14 of the Public Order Act.