EDF has insisted that its plans to complete the £18bn Hinkley Point C nuclear power station in Somerset by 2025 remain on track, despite reports that some of its engineers had called for a two-year delay and a redesign.

It came as an EDF board member representing senior staff said in a letter to employees that he would vote against the controversial project. Christian Taxil, who represents the managers’ union CFE-CGC, is the first board member to go public with doubts about the project.

The Financial Times reported that senior engineers at the French energy company had supported a wait of at least two years on the project because of its complexity and advocated a redesign of the reactor technology to make it smaller and cheaper to build.

In an internal white paper sent to top executives and seen by the FT, the engineers argued that the “realistic service date was 2027”.

But in a statement emailed to Reuters on Wednesday, EDF, which is the 85% owned by the French government, dismissed “unfounded rumours and fantasy information” in the media. “EDF denies these rumours [and] confirms that the start up date for the first reactor is fixed for 2025 and that no delay is envisaged,” the company said.

Taxil said EDF should not launch the project now because of difficult power market conditions, technical problems with the two planned reactors and EDF’s weak financial position. He wrote in the letter to staff: “Today, conditions are not right for me to give a positive opinion if such a project were presented to me.”

There are growing signs of opposition to the project within EDF, including the resignation of its finance director. The company’s chief executive, Jean-Bernard Lévy, has written to staff insisting that it needed more financial backing from the state and would not go ahead without this.

The six union members on EDF’s 18-person board are expected to vote against Hinkley Point. They believe that it is too expensive and a risk to the company’s future; EDF is struggling with rising debts. While some non-union board members have voiced doubts about the project in private, all are expected to vote with the management when the board meets on 11 May to make a final decision on the project.

A new nuclear reactor at Hinkley in Somerset has been heavily promoted by the chancellor, George Osborne, and other ministers as key to keeping the lights on in Britain. The last of the UK’s coal-fired power stations is due to close in 2025.