The deal will add millions to the labour bill for the job with around 6,000 workers expected on site during the peak of construction.

Strike threats have hit the site following a row over bonuses on the job.

But “constructive discussions” are now under way after client EDF stepped in between the unions and contractors.

All side have now agreed to take part in a collective differences panel that will seek to identify an agreeable long-term settlement of the bonus issue.

As part of the agreement, interim bonus payments will apply until the end of August 2017.

Working supervisors and craft grades will get an extra £4 an hour, skilled worker grades £3 per hour and general workers £2 an hour.

The interim payments were agreed by representatives of EDF Energy, BYLOR (the Tier 1 contractor comprising Laing O’Rourke and Bouygues TP), the Kier-Bam joint venture (who are undertaking the enabling works) and Unite the union.

As part of the agreement, the previously approved Civil Engineering Sector Agreement (CESA) for the project, which governs pay and conditions, will be fully implemented with effect from 1 June 2017, including the interim bonus arrangements.

The collective differences panel, which will consist of a senior Unite full time official and a senior EDF Energy executive, will thoroughly examine the matter of bonuses.

The panel will seek to identify appropriate permanent bonus arrangements that are agreeable to all parties and is scheduled to deliver its recommendations on productivity/milestones bonus payments by August.

As part of the agreement, no industrial action will be considered while these interim arrangements are in place or until the collective differences procedure has been exhausted.

Nigel Cann, EDF Energy’s Programme and Construction Delivery Director for Hinkley Point C, said: “We are proud about the ‘best in class’ nature of the overall package for the Hinkley Point C civil workforce.

“We have created great facilities, an opportunity to develop and a very competitive reward structure.

“We are pleased that these interim arrangements allow constructive dialogue to continue to finalise this important agreement.

“Unite the Union has been a constructive partner in the discussions to date and I look forward to this continuing throughout the construction of the Hinkley Point C power station.”

Unite acting national officer for construction Jerry Swain, said: “I am pleased that following consultation with our stewards and members that we along with the various parties have been able to agree a clear path forward and that the prospect of industrial action, which is always a last resort, can be taken off the agenda in order to allow the ‘Differences Panel’ to deliberate.

“The work undertaken by EDF Energy in ensuring that all parties signed up to the interim agreement has been crucial in providing a breathing space and creating the opportunity for a long-term solution being agreed to finally resolve this matter.”

One industrial relations expert said: “It seems the client has stepped in to get this sorted.

“But it’s a bit odd now the unions are talking directly to the client rather than the contractors.

“This could see the wage bill rise enormously.”