By Nick Assinder
Political correspondent, BBC News website
The government's conversion to nuclear power represents one of the most significant about-turns of any administration in recent times.
But what has driven the prime minister's apparent rush towards the creation of a new generation of nuclear stations which, in the 1997 election manifesto, he had ruled out?
Ministers insist nuclear power is a must
In that document, and in the wake of widespread public unease about all things nuclear, he bluntly stated there was no economic case for any more such stations.
Just over half way through his reign, in the 2003 energy white paper, he still thought nuclear power plants were an "unattractive option", but ministers carefully left the door open for a future change of mind, if circumstances required it.
There would, however, be no change of policy without "the fullest possible public consultation".
Now Mr Blair leaves Downing Street fiercely arguing that circumstances have indeed changed and that without new nuclear capacity Britain could soon face an energy crisis.
Meanwhile, he has been forced by the courts to re-launch consultation on the issue after the original process was ruled to have been "wholly insufficient" to allow people to make intelligent responses.
Government wants a mixture of nuclear and renewables
However, it has already been made clear that the new consultation will make no difference whatsoever to the government's pro-nuclear stance.
Now, in an article in the Times newspaper, Mr Blair has gone so far as to state: "Over 10 years I have watched energy policy go from being a relatively quiet backwater to something taking on a strategic importance that could be as crucial to our country's future as defence".
What, then, has been the reason for this apparently extraordinary change of heart?
It could almost be summed up in a single word - Russia.
The reason for that, as Mr Blair put it, is that Russia could use its energy supplies to the west as "an instrument of policy".
But it is not a direct threat from Russia as much as the way its flexing of energy muscle in Eastern Europe in recent years has made it a good symbol of what might happen after Britain becomes a net importer rather than exporter of energy in 2020 from countries in Europe and the Middle East.
Mr Blair argues that Britain needs to remain self-sufficient and that will require a mix of renewables and nuclear.
Neither, however, is this to say that climate change is not also being cited as another circumstance that has changed.
Trade and Industry Secretary Alistair Darling has admitted he, too, is a convert to nuclear, saying the switch is not only necessary to secure future supplies, but also to cut emissions.
"If we knock out nuclear and say no more under any circumstances, that means we will have to import more gas and we run the risk of putting more and more carbon into the atmosphere."
Green groups don't buy much of this argument, claiming that by focusing investment on nuclear, it will be squeezed out of renewable projects and that, in any case, such alternatives are not being given sufficient encouragement.
These arguments will continue to rage - Gordon Brown is not about to abandon the new policy - although it is likely the issue of security will be given increasing prominence.
The future, however, looks certain to be nuclear.