Nuclear power in the UK has turned out much safer than environmentalists worried it would be.

Friends of the Earth, which feared the threat of a catastrophic Chernobyl-style meltdown in the UK, is now less concerned. Fear of nuclear armageddon was a driving force for the green movement in the UK – Greenpeace has its name for a reason.

But Friends of the Earth have revealed that their old ideological opposition to nuclear has crumbled, to be replaced by a new pragmatic opposition based on cost and build time.

In the old days nuclear was fought because of the health threat; now it’s opposed because it’s the wrong option in an energy system designed to tackle climate change.

The group denies that its position has shifted – but to me this looks a huge and significant shift – and especially controversial if you work for the UK nuclear industry and have been told for decades that your operations are a clear and present danger to the public.

The new position was expressed in an interview with Friends of the Earth’s campaigns director Craig Bennett on Radio 4’s Today Programme on Wednesday.

When the presenter asked him to explain the group’s opposition to nuclear power stations he got this reply: “The biggest risk of nuclear power is that it takes far too long to build, it’s far too costly, and distorts the national grid by creating an old model of centralised power generation.”

I sat up in bed. Friends of the Earth says the biggest risks of nuclear are that it’s too slow to build; it’s too dear, and would you believe it… it even distorts the grid!

The presenter Justin Rowlatt interrupted, sounding surprised: “You’re not worried about the risks from radiation?”

Bennett replied:

Of course, there are real concerns about radiation, particularly around nuclear waste… but I think it is important how this debate has shifted down the years.

The real concern now is how we get on fast with de-carbonising our electricity supply. It’s very clear that nuclear can’t deliver big changes fast.

That’s a huge risk if we’re trying to tackle climate change. With renewable technologies and with energy efficiency we could be making a difference within three or four years.

So, presented with a free hit against the risk of a nuclear accident, Friends of the Earth’s green warrior swiped at build-time, cost and grid disruption. Further prompted on safety he swiftly shifted to the intractable problem of waste, and did not mention accidents at all.

Does that mean if nuclear stations were cheap and quick to build and we could bury the waste somewhere, nuclear would become respectable? Well, the group told me later they were just as concerned about accidents as ever – but the cat was out of the green bag.

Friends of the Earth’s shift was signalled in a little-reported policy paper last year which included an independent assessment that coal and maybe even gas generation presented more health risks than nuclear. I have not heard the shift so strikingly articulated before this week.

The group’s phones started ringing after I broadcast a news item on their policy shift on Wednesday morning.

The matter is highly delicate: the group is locked in an internal battle: some members want it to accept nuclear’s role in the UK’s low-carbon energy mix, whilst others are as passionately anti-nuclear as in the old days of the cold war and nuclear armageddon.

Andy Atkins, its director, said on its website: “Friends of the Earth is certainly not now pro-nuclear, we have not changed our position.”

Now, I have been tracking the environment movement for 25 years, but to confirm my memory on Friends of the Earth’s historic position I phoned its former director, Tony Juniper. He told me: “In the UK the (nuclear) safety record has been pretty good, so the safety dimension has diminished - and the emphasis in Friends of the Earth has changed.”

He said in the early days of the green movement, campaigners opposed the nexus of civilian and military nuclear, but the cold war ended and old accidents at Dounreay in 1977 and Windscale in 1957 receded into memory.

Bennett later told me:

Perhaps in the past our opposition to nuclear was gut instinct.

Our position has now been “refreshed”. We don’t want to close down the UK nuclear industry right away – that would create far too many problems for energy supply over coming decades. But we still very much oppose nuclear new-build. The biggest issue is cost.

Bennett told me Friends of the Earth had always deployed a suite of arguments against nuclear power, with the emphasis shifting over time.

He was supported by Tom Burke, another former head of Friends of the Earth, who remains strongly anti-nuclear. He says the group’s fundamental opposition to nuclear through the decades has not changed - he says the main thrust of Friends of the Earth’s attack against the industry has fluctuated as different priorities emerged.

Other environmentalists, though, have been happy to credit the UK nuclear industry with its safety record – even in some cases to reluctantly embrace the previously hated industry as an ally in the fight against climate change.

Stephen Tindale, former Friends of the Earth campaigner and former head of Greenpeace, is a nuclear convert. He told me Friends of the Earth’s position had inarguably changed:

Friends of the Earth campaigned to get existing nuclear stations closed down, on safety grounds, as well as opposing new nuclear stations. So the current Friends of the Earth line is a change from the past. And the reason for opposing new nuclear is now cost rather than safety.

A change of emphasis, which Tony Juniper accepts has happened, is a change in the campaign. Refreshing a campaign, to use Craig’s word, is a change in the campaign - no point in “refreshing” but leaving it just the same. Friends of the Earth is not pro-nuclear now, but it is less strongly anti-nuclear and on different grounds.

I’m still nuke agnostic but for years I have considered nuclear economics more controversial than nuclear safety in the UK, so I’m happy to see the debate move to that ground. Friends of the Earth’s opposition is now less ideological and more functional and that marks a maturing of the green movement which should be celebrated by Friends of the Earth, not denied.

I suggest a new rallying cry: “No nuclear new-build – it distorts the National Grid!”