French finance authorities have raided the offices of EDF just days before the state-backed energy giant is expected to give the go-ahead to its controversial Hinkley Point new nuclear project.

The long-awaited final decision on the Hinkley project is scheduled to take place at a board meeting next Thursday, even as authorities in both the UK and France escalate concerns over the costs of the £18bn project.

French investigators from the Financial Markets Authority (AMF) swooped on EDF’s Paris headquarters on Thursday morning as part of a probe into EDF’s disclosure of information to the market. Investigators are said to be concerned about the reporting of its domestic nuclear maintenance costs as well as the plans to develop new nuclear reactors in Somerset.

Local media reports say the AMF recovered a series of documents from the EDF offices and requested a meeting with EDF general secretary Pierre Todorov.

Just hours after the raid the company said it would hold a board meeting on Thursday 28 July to agree a final decision on the project, feeding speculation that the company is preparing to push ahead with the 3.2GW project.

The company also has a scheduled extraordinary general meeting on Tuesday next week, seeking approval from shareholders for its proposed £3bn recapitalistion.

Meanwhile, the head of the UK’s National Audit Office has raised further concerns over the UK’s plans to subside EDF’s plans in the face of a “tidal wave” of pressures from an impending Brexit and a pipeline of existing infrastructure projects requiring a total of £405bn.

Sir Amyas Morse, comptroller and auditor general at the NAO, told the Guardian in an interview that projects such as the Hinkley Point C nuclear plant, a third runway at Heathrow and the ambitious HS2 rail project would have to be reassessed as the government decides which can be done without, according to a report in the Guardian.

“We need to ask ourselves, can the public sector deliver Hinkley Point C, a third runway, HS2, a Northern Powerhouse, nuclear decommissioning, Trident renewal and restoration and renewal of the Palace of Westminster all at the same time?” asked Sir Amyas.

“There is a policy at the moment to have lots of infrastructure projects. I say fine, but some of them will have very big consequences in terms of your ability to deliver your other goals,” he said.

In a recent report, the NAO heaped criticism on the Hinkley Point plans saying the spiralling costs will hit consumers in the pocket, even as other low carbon energy options offer an increasingly better deal.

The subsidy bill to be paid by households and businesses for Hinkley Point has more than quadrupled since the agreement for the new nuclear plant was signed in 2013.

At the time the deal was signed, power price projections had implied a lifetime cost to consumers of £6.1bn for the subsidies. But as of March this year, that had more than quadrupled to £29.7bn due to significant cuts to official power price forecasts.

EDF declined to comment on the raid, and the AMF was unavailable.