Anti-incinerator campaigners have hailed what they say could be a game-changing moment in the battle against a waste burner in Norfolk, after the leader of Norwich City Council wrote to the environment secretary to make clear the authority does not support such plants.

It had been understood that, after letters supporting the plant were sent to her by the leaders of a string of district councils in Norfolk, environment secretary Caroline Spelman was set to release �169m of government funding to Norfolk County Council for the �500m incinerator in King's Lynn.

In November she with-held the Private Finance Credits for the Saddlebow plant, saying she needed the county council to convince her that there was 'broad support' for the scheme.

But, with the leader of an authority which generates about a quarter of the county's waste having written to stress the city council is not in favour of waste being tackled through incineration, campaigners claim the environment secretary no longer has the evidence of that 'broad support', so should not award the credits.

City council leader Brenda Arthur's letter, sent yesterday, makes clear that City Hall's position on incineration has not changed since previous proposals for one to be built in Costessey were discussed in 2007.

The council passed a motion then that the authority was against any form of waste treatment which involved incineration.

Earlier yesterday, Green and Liberal Democrat city councillors collectively wrote to Ms Arthur and Norwich City Council chief executive Laura McGillivray urging them to write to Mrs Spelman to point out City Hall's opposition.

Mrs Arthur insisted she had been planning to pen a letter anyway and it was not that pressure which made her do so.

She said: 'I would have thought our position was very clear, given the motion we agreed has been in the public domain since 2007.

'I thought our view was out there long before all this started, so I had not felt the need to write before now. 'I had waited because, as I made clear to the leader of the Green group over the weekend, I was due for a briefing at City Hall yesterday morning to make sure nothing had changed since the motion was originally passed.'

Liz Truss, South West Norfolk MP, said last week that she feared Mrs Spelman was on the brink of awarding the credits based on the letters of support she had received from councils such as South Norfolk, Broadland, North Norfolk and Breckland Council leader William Nunn, who sent his as the chairman of the Norfolk Waste Partnership.

Those letters sparked controversy and complaints from some opposition councillors that the leaders had acted without putting the matter to their respective councils.

Nick Daubney, leader of West Norfolk Council, which organised a poll showing 65,000 people were against the incinerator, had sent his own letter to Mrs Spelman urging her not to award the credits.

And he said the city council's restatement of its opposition to incinerators should convince Mrs Spelman not to award the credits.

He said: 'I feel Mrs Spelman was taking the silence from the city council as support, but we now have the two main urban centres in Norfolk saying that this is wrong. How can that demonstrate broad consensus?

'I think Mrs Spelman needs to talk to us. I'm happy to sit down with her, the two MPs and [county council leader] Derrick Murphy face to face.

'We are calling on legal advice here, because this decision needs to be based on the criteria which has been set down.

'I know people have been calling on us to launch a judicial review, but you can only go down that route once. However, I think she needs to know it is our firm belief that if she awards the credits against the criteria which has been laid down, that is a risk she could face.'

Environmental consultant Richard Burton, who has long opposed the incinerator, said: 'With clear opposition from both the council that would host the incinerator (West Norfolk) and the council that takes County Hall's own waste (Norwich), it would now indeed represent a tearing up of the PFI rules should the secretary of state release the credits.'

Mike Knights, deputy chairman of King's Lynn Without INcineration (KLWIN), said: 'It would have been nice to have had this letter sent a bit sooner, but I am very grateful that it has been done.

'The county council has relied on the silence from Norwich City Council being interpreted as them being in favour and they cannot pretend that anymore as it is in black and white that they are against it.

'If PFI money is now awarded then DEFRA would be very vulnerable to a High Court challenge, as it goes against their own criteria of needing broad support.'

The county council, which says the plant would save millions of pounds a year, agreed in March last year to award the contract for the incinerator to Cory Wheelabrator, but it has yet to be signed.

The council's planning committee, which will decide whether to grant permission for the plant, last week agreed it would need to visit the site ahead of any decision.

Bill Borrett, cabinet member for environment and waste at Norfolk County Council, said: 'The sending of such a letter at this very late stage of this project cannot be coincidental.

'I can fully imagine the pressure that Brenda Arthur, as leader of a minority administration at City Hall, is under from campaigners via the Green Party in particular.

'However I am disappointed at this 11th hour flurry of activity since she personally attended a meeting of the Norfolk Waste Partnership on December 19 and raised no objections to the Willows proposal or the strategy. 'Neither did she do so when openly challenged through questions at her own council meeting in November - just six weeks ago.

'In addition, I was at the September meeting of the Norfolk Waste Management Partnership when Norwich reaffirmed its continuing support for the waste strategy's nine objectives.

'I am disappointed at this last minute intervention, but not surprised because of the political state of play in the city. '

dan.grimmer@archant.co.uk