When Hinkley Point was first talked about in the mid-2000s, Tony Blair was prime minister, the UK’s position in the EU looked secure and the project was being run by British Energy.

On Thursday night board members at EDF, the French utility now running the project, decided to give the scheme the final go-ahead, but they did so against a completely different political backdrop. The UK is on its third prime minister since Mr Blair, it is on its way out of the EU and British Energy is no longer.

Nothing more clearly illustrates the change in political background than the decision by UK ministers, immediately after news of the French approval, to delay the project once more, with officials saying Theresa May wants to examine the case in full, having become prime minister this month.

It is not only the political background that has changed since Mr Blair’s government first started talking of the UK’s “nuclear renaissance”. The project itself has become far more protracted and expensive than it was ever supposed to be.

The problems started early on in the life of the scheme.

EDF bought out British Energy for £12.4bn in 2009 and, with it, acquired the company’s eight new nuclear sites. Even then, however, it appeared the timetable was slipping.

Vincent de Rivaz, chief executive of EDF in the UK, had said he expected Britons to be cooking their Christmas turkeys using power from the first new nuclear plant by 2017. But by late 2008 the company was talking about 2018, while British ministers were saying it would be finished “well before the 2020s”.

The main reason for the slipping timetable was that a nuclear power plant of the same design was being built in Olkiluoto in Finland, and that project was proving harder and costlier to build than anyone had expected.

The design, known as the European Pressurised Reactor, was supposed to be the safest in the world, built to withstand even a terrorist flying a commercial aeroplane into it. But it was these complex and expensive safety measures, experts say, that have seen the EPR delayed almost everywhere it is being built.

In 2013, EDF suffered a significant setback to its plans when Centrica, a co-investor in the project, pulled out. Iain Conn, Centrica’s current chief executive, sounded a sceptical note on the scheme on Thursday, just hours before the EDF board meeting. “It is an expensive way to get electricity,” he said.

Centrica was replaced by CGN, a Chinese state-backed nuclear power group.

At around the same time, EDF executives commissioned a report from auditors in the company about the likelihood that Hinkley Point could be built on time and on budget. That document, which was called the “Cardiff report” and which the Financial Times has seen, warned that there was only a 50 per cent chance that it could be produced for its £16bn price tag.

The report, which one board member said they had not been shown, recommended a budget of £18bn — a figure that was accepted by the company only in 2015.

Despite all these problems, one thing that remained secure about Hinkley Point — until last night — was political support for the scheme on both sides of the Channel.

In the UK, where ageing coal power stations are closing faster than the government expected, ministers showed their support in 2013 by agreeing to pay £92.50 for every megawatt-hour of electricity Hinkley Point produces. The current wholesale price is around £40.

London’s decision last night to hold yet another review of the project shows how much has changed since the UK voted to leave the EU and David Cameron, one of the scheme’s biggest backers, resigned as prime minister. Officials said Mrs May’s cautious approach lies behind the delay but the company will now worry that the political consensus could soon break.

We aren’t supposed to be spokespeople for a union or the state. I’m really ill at ease with this project

Paris, however, remains fully committed, with ministers seeing Hinkley Point as crucial to maintaining the competencies of the French nuclear sector and supporting its suppliers.

Until the last-minute UK intervention, that political support had driven the project to the finishing line in the face of a host of delays and potential obstructions. Those delays included opposition from within the board, which was more divided than had been expected.

Before Thursday’s meeting, the project had led to the resignations of two senior people within EDF. The first was Thomas Piquemal as chief financial officer, the second, Gérard Magnin, a state representative on the board. And even after those resignations, opposition remained.

As the board prepared to meeting on Thursday afternoon, one director told the Financial Times: “We aren’t supposed to be spokespeople for a union or the state. I’m really ill at ease with this project.”

The announcement by Greg Clark, the business and energy secretary, late last night, to delay the project once more, suggests that person is not alone.