Just one bidder is left in the race to build the contested Edmonton incinerator, sparking concerns about the absence of competition in the tender process to rebuild a plant to burn north London's waste.

The estimated £683m contract wasn't due to be awarded until spring 2022, after a gruelling 14-month competitive tender.

But the Gazette can reveal that one of the three bidders – French company CNIM – has pulled out, and the other two – Spanish firm Acciona and Swiss firm Hitachi Zosen Inova – are going to work together, effectively meaning there is just one contender left.

Asked the move means going back to square one of the bidding process to find a firm to design, procure, construct, commission and test a new plant – but a North London Waste Authority (NLWA) spokesperson said the fact that there is effectively just one bidder left does not contravene procurement rules.

The cost for the entire North London Heat and Power project, which includes a recycling facility, has already spiralled, with estimates nearly doubling in 2019, from £650m to £1.2bn.

Taxpayers from the seven London boroughs – Hackney, Islington, Barnet, Camden, Enfield, Haringey and Waltham Forest – that make up the NLWA, will foot the final bill.

The NLWA claims the existing 50-year-old incinerator is "coming to the end of its operational life" and wants to replace it with an "energy recovery facility" (ERF) to generate energy to heat homes by burning rubbish.

Campaigners are worried that what would be one of the biggest incinerators in Europe could soon become obsolete, locking north London into decades of low recycling rates, air pollution and greenhouse gas emissions.

Carina Millstone, co-founder of Stop the Edmonton Incinerator Now, branded the withdrawal of CNIM from the race a "major victory" in their campaign – but also said it raised concerns there was no longer a competitive process.

Acting as spokesperson for 27 environmental, community and political groups including XR Zero Waste and Greenpeace, she called on the remaining two firms to follow suit and pull out.

"The fact that the NLWA still intends to proceed with its plans with only one contractor poses serious concerns for value for money," said Ms Millstone.

"It's no longer a competitive process if there's only one bidder. They could raise their price – but we don't want to see it built at all," she added.

This paper contacted all three bidders, who have all declined to comment.

In 2020, Robert Sedgman, commercial lead for the NLHPP, outlined the 14-month process the three shortlisted bidders would have gone through.

Initially they were due to spend five months developing detailed bids. Following their submission, each of the three contenders were to be assessed on three criteria - namely their technical ability to make sure the incinerator meets performance standards, how they fared commercially, and on quality and management standards.

There should then to have been an "intense" six months' dialogue between the NLWA and each bidder, before they were given four months to submit a final tender.

The authority scheduled in two months to evaluate them all, a further month going through internal approvals and asking its members sanction and sign a contract before, finally, notifying the successful bidder next spring, ahead of building starting in the summer.

A spokesperson for the NLWA said just having one bidder left was now "allowing a detailed and intense dialogue phase of the procurement to be undertaken, ensuring that plans and costs are subject to the most thorough exploration to achieve a successful outcome for north London’s residents".

They said: "We are confident that the procurement process, following all requirements of the Public Contract Regulations 2015 and delivering value for money, will enable a decision for the ERF contract award to be made, in line with our programme for delivering this world-class project.

"In all its actions NLWA ensures compliance with legal obligations and the delivery of value for money for council tax payers."

Ms Millstone said campaigners will exert pressure on the remaining consortium firms to urge them to pull out.

""If no one wants to build it, it's clearly one of the ways it can be stopped," she said.

"Acciona has a very strong brand identity, and strong commitment to sustainability so we feel the project is at odds with their other portfolio around renewable energy.

"We are reasonably hopeful we can get them to reconsider and pull out, and if they don't we might have to escalate and see if they will reconsider then."