A new war of words has broken out between London and Edinburgh over the prestigious COP26 green summit with fears that Glasgow could lose staging it because of the “ridiculous” over-inflated policing costs for the global event.

One well-placed source with knowledge of the preparations for the UN-sponsored summit said the UK Government was as recently as last week “actively considering” two alternative venues in England.

Suggestions that Nicola Sturgeon would be to blame for any switch of the venue to London’s docklands was dismissed as “nonsense” by the Scottish Government, which said Whitehall insiders were seeking to undermine COP26 in Glasgow.

When asked if the Glasgow venue was under threat, No 10 responded by repeatedly stressing how Boris Johnson was “committed” to keeping the event at the Scottish Events Campus in the city; earmarking an alternative site, it explained, in this case the Excel Centre in London’s docklands, was just “standard practice” for such a large international event.

On Tuesday, the First Minister called for relations between London and Edinburgh to be “reset” and for the squabbling between the two administrations to end.

The UK Government welcomed Ms Sturgeon’s olive branch and said the two administrations could now “move on and make a success of COP26”.

But one well-placed source, close to the summit preparations, told The Herald: “The Cabinet Office as of last week was actively considering two English venues for the COP.

“Even if Nicola starts behaving, the estimated policing costs are off by £100m-plus.”

Talks are continuing over the policing costs, said to be north of £200m, according to sources. Downing St stressed that what was at the forefront of the Prime Minister’s mind was value for taxpayers’ money and that the costs had to be “realistic”.

One Whitehall insider noted: “Losing the Glasgow venue was the reason for Sturgeon’s sudden change in tone. The costs they have put forward for policing have been ridiculous. It’s good they are talking more constructively.”

Asked directly if there was a risk to the Glasgow venue, Mr Johnson’s Press Secretary said: "We are committed to holding COP26 in Glasgow but the Scottish Government need to work with us to make sure this is a successful summit which showcases the UK as a world leader in tackling climate change and represents value for the UK taxpayer."

Pressed if the venue could be moved, he replied: “I’m sure COP26 in Glasgow will be a tremendous success; to deliver on that it’s important we work closely with the Scottish Government.”

He pointed out: “The FM said yesterday that the Scottish Government would work closely and constructively with the UK Government to deliver COP26,” and again stressed: “We are very keen the summit represents value for taxpayers’ money.”

Asked for Mr Johnson’s response to Ms Sturgeon’s call to reset relations, the Press Secretary insisted: “This issue is above party politics.”

But last night a spokeswoman for Roseanna Cunningham, the Environment Secretary, said: “Estimates of policing costs are made by Police Scotland and the SPA on the information available to them from the UK Government, they have not been calculated by the Scottish Government and the First Minister – rightly – has no part in them, so it appears UK Government sources are simply making things up in order to undermine COP26 in Glasgow for which there is huge enthusiasm.

“Everyone in Scotland is focused on making this event a success and doing what we can to help reach a global commitment to net-zero and we can only hope that the appointment of a new COP President will put an end to this nonsense and see the Prime Minister respond positively to the First Minister’s offer of ministerial attendance at COP planning and Cabinet meetings to help the successful delivery of the event,” she added.

London and Edinburgh have been arguing over COP26 for months.

The Scottish Government has been embroiled in a row with the UK Government over use of the Glasgow Science Centre, which it had earmarked for its summit pavilion but which now Whitehall wants as part of the climate change event.

Downing St forcefully denied a claim that Mr Johnson had referred to the FM as “that bloody wee Jimmy Krankie woman”.

The FM has derided the focus on such talk, insisting that what should be the primary focus was saving the planet. “There are plenty of issues Boris Johnson and I can have squabbles about, this really, really should not be one of them,” she declared.

Ms Sturgeon has spoken of having made “crystal clear” her Government’s commitment to COP26 and that there was a “shared responsibility” for making it a success.

She has raised the prospect of Roseanna Cunningham, the Scottish Government’s Environment Secretary, attending Mr Johnson’s Cabinet and Cabinet sub-committee meetings on climate change. But as yet she does not appear to have had a response from the PM.

Ms Sturgeon said: "If he insists on playing politics it will be on him, not me."

Today as he reshuffles his Cabinet, Mr Johnson is also expected to name the new COP26 President to replace Claire Perry O’Neill, who was sacked earlier this month. No 10 has insisted it has to be a ministerial “big hitter,” who can command the international stage. Michael Gove, the Cabinet Office Minister, has been tipped for the role.