EDF could start building Britain’s first new nuclear power station in more than 20 years before it receives full planning permission.

Full site licenses for the new nuclear plants are not due to be awarded before 2013 following completion of a detailed planning and safety study into the proposed reactor technology.

But EDF is currently drawing up plans to start preliminary work on two sites it has earmarked for new reactors at Hinkley Point in Somerset and Sizewell in Suffolk well before that date.

In a statement to The Times, EDF said it was planning “to carry out a range of pre-construction preparatory work before 2013”.

This could include levelling the ground, the erection of flood barriers as well as excavation work to prepare the foundations for the new plants.

EDF insisted it would “only undertake work for which it has all the necessary approvals”.

Nevertheless, the plans provoked a backlash from opponents of the industry.

“We think any actions that the industry takes before the proper licenses are in place are inappropriate,” said Jean McSorley, nuclear campaigner at Greenpeace.

She also said there was evidence that EDF had started placing orders for reactor components for use in the UK market, despite the fact that the French design it plans to use has not yet been approved by Britain’s safety regulator.

EDF, which is 85 per cent controlled by the French state, has a highly ambitious timetable for construction of the new plants.

It wants to build at least four new reactors in the UK with two at each site and is planning for the first of these, probably at Hinkley Point, to be operational in 2017.

Critics have said this is unachievable given the extreme complexity of the construction work and the need to observe rigorous safety standards.

The company warned earlier this year that it would "not tolerate" significant planning delays of the kind that have plagued other major infrastructure developments in the past.

The last nuclear power plant to be built in the UK, Sizewell B, took 12 years to build because of lengthy planning delays.

The planning inquiry for Heathrow Terminal Five also delayed construction for several years.

EDF views an early start to construction before full consent has been granted as a critical way of accelerating the programme and meeting its internal deadlines.

The low-lying coastal site at Sizewell, in particular, is expected to require significant preparatory work before full construction can begin in order to protect it against flood risks.

“Of course it will all be at their own risk,” said one industry source.

“If they were refused a site license it would be at their financial loss.”

EDF, which bought UK nuclear generator British Energy last year, is leading the race to build a fleet of new nuclear reactors in the UK.

The current fleet of eight plants generate nearly 20 per cent of UK electricity but all but one of them are due to be retired from service between now and 2025.

A spokesman for the Department for Energy and Climate Change said that no work on the actual nuclear plant could commence before special consent had been obtained to do so.

He said any preliminary work a company started doing before that date, even with local authority permission, would “have no bearing on the eventual decision on consent” for a nuclear power station.

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