British regulators have approved the design of a new generation of nuclear power reactor as the French companies seeking to build it have delayed their plans.

Britain's Office for Nuclear Regulation and Environment Agency Thursday said they have signed off on design specifications for the type of "European pressurized water reactor" proposed by EDF and Areva after a five-year review.

"We are satisfied that this reactor is suitable for construction in the U.K.," Colin Patchett, acting chief inspector of nuclear installations for the ONR, said in a statement. "It is a significant step and ensures that this reactor meets the high standards that we insist upon.

"We have been able to identify significant issues while the designs are on the drawing board."

Joe McHugh, the British Environment Agency's head of radioactive substances regulation, concurred, saying the decision was made after long years of studying the "U.K. EPR" design.

"We set out with ONR to rigorously, and transparently, assess whether this new reactor design, the U.K. EPR, would be acceptable for use in England and Wales," he said. "Through robust scrutiny we are satisfied that this design can meet the high standards of safety, security, environmental protection and waste management that we and ONR require."

EDF and Areva are seeking to build two new plants utilizing the EPR reactors at Hinkley Point in Somerset -- a 3.3-gigawatt project likely to cost at least $22 billion and which is being counted on by the British government to deliver on its goal of adding new nuclear capacity by 2020.

The approval process began in 2007 and was delayed following last year's Fukushima nuclear disaster in Japan, which required 16 changes to the U.K. EPR, including additional flood protection measures and the provision of mobile generators and pumping equipment, the BBC reported.

"The acceptance of the design for the EPR reactor is a major achievement and milestone for our new nuclear project in Somerset," EDF Energy Chief Executive Vincent de Rivaz said. "It highlights our credibility and that of the EPR design, as well as demonstrating that the U.K. has a credible policy and regulatory framework in place."

The news, however, came as concerns about the costs of the project have mounted as EDF's prototype of the EPR reactor at Flamanville in Normandy, France, have jumped nearly $3 billion to $11.2 billion due to post-Fukushima changes, the BBC said.

One of its partners at Flamanville, Italy's Enel, later announced it was pulling out of the effort.

EDF also revealed this month its decision on a final investment at Hinkley -- originally hoped for by the end of this year -- has been pushed back until "the earlier possible date."

The British newspaper The Guardian, citing sources close to the project, reported this month the decision is unlikely to be announced before April even as British Energy Minister Ed Davey has fast-tracked negotiations to set a guaranteed price for EDF and Areva before the end of the year.

The project is also facing opposition by anti-nuclear activists, who in September staged a protest at the existing nuclear reactors at the Hinkley site.

Four people were arrested and charged with willfully obstructing a highway leading to the plant during a Nov. 23 protest in which 10 activists erected a blockade in an attempt to keep workers from clearing ground in preparation for the new reactors, ITV reported.