WHEN Tony Blair promised on Tuesday to put the building of nuclear power stations "back on the agenda'' few people doubted that this was effectively a green light that Britain would construct a new generation of reactors.

Although an energy review is not due for publication until July, the industry believes that, one way of another, the prime minister is intent on building more stations as the way to guarantee energy supplies and tackle climate change.

According to someone who has advised the Government's energy policy makers: "There's a mood in Whitehall that more nuclear stations are the answer. It's the way things are going. I think Britain will get them.''

Yesterday, Areva, the French state-controlled group and the world's largest builder of nuclear power stations, effectively threw its hat into the ring, saying that it could have a new series of reactors up and running by 2017.

Areva stands a good chance of getting any nuclear design and build contacts - as the only serious rival, according to energy experts, is Westinghouse, the US-based but Japanese-owned company.

AECL, a Canadian company, has an outside chance of winning contracts, but energy insiders say the Government has already declared a preference for the PWRs - pressurised water reactors - of Areva and Westinghouse.

The UK effectively ended its expertise in building reactors when British Nuclear Fuels sold Westinghouse to Toshiba for $5.4bn. It is, though, unlikely that the Government would award contracts without insisting that UK companies played some part in any construction consortium.

Amec, the UK engineering group, has nuclear project management and decommissioning experience, but for one observer the firm "has no pedigree in building power stations. Work on this would have to go abroad''.

Costain is another UK firm that could get a project management role. But, again, foreign firms, such as America's Bechtel, are seen as having more experience in this area.

So, as well as the political and regulatory hurdles of embarking on a nuclear-build programme, this lack of indigenous experience could also be a problem. British experts in the nuclear field are a dwindling breed.

According to Prof Ian Fells, a leading expert on the industry: "The teams of engineers that built Sizewell B in 1995 are all retired or dead. We do not have the skills to build nuclear power stations any more.''

Although there is no immediate urgency to begin a new nuclear programme, the industry believes that planning and setting a timetable would have to start within three or four years if the UK is to meet climate change targets and prepare for the run-down of gas and oil stocks.

"That would at least give time to start building up the knowledge base and bring back skills that have laid dormant,'' said an Amec spokesman. "There are still a lot of young scientists coming into the industry.''

Although small power stations are being phased out, the first big closures, including Hunterston B and Hinkley Point B, start being decommissioned in 2011, with the rest being taken out of service by about 2023.

It is estimated that there is a need for up to 10 new stations, though it is thought that the UK could build only two simultaneously. When Areva spoke yesterday of building "a series'' of reactors by 2017, the number in mind was probably at least four, which would keep the costs low.

The capital cost of a new nuclear plant depends on how quickly the reactor can be built and whether economies of scale can be achieved. Using a modular design will cut costs if several reactors are built in sequence.

A nuclear station that Areva is building at Olkiluoto, in Finland, is thought to cost about pounds 2bn to pounds 3bn. But a series of four reactors, each using the same design, might cost as little as pounds 1.2bn per plant.

A modern PWR reactor should take about five years to build, but could be as long as 10 years if unexpected project delays are factored in - sending the interest payments on the capital investment soaring. In comparison a gas-fired power station can be built in around six to 18 months, so interest payments are less of a problem.

In Finland, the backers of the Olkiluto nuclear project recently admitted that it was about nine months behind schedule despite being only one year into the construction programme.

It is possible that any new UK reactors would be built on the sites of existing power stations, which would cut down on planning delays. But, as the UK has found with many large-scale construction projects, it has a poor record meeting deadlines.

At least the taxpayer won't be expected to pick up the direct cost of a nuclear-build programme. The Government has made it clear that the market - the power station construction companies and the distributors who will buy the electricity - will be expected to meet the costs.