Papers to go before the Scottish Police Authority (SPA) board on Friday have outlined the potential cost of the United Nations Cop26 summit, which will bring heads of state from nearly 200 countries to Scotland in November.
According to the documents, “dialogue remains ongoing” with Westminster over who will foot the bill for security.
The conference has been described as the most important global gathering on climate change since the Paris agreement was signed in 2015.
The two-week event will be the largest summit the nation has ever hosted, with up to 15,000 people flocking to Glasgow’s Scottish Events Campus (SEC) on the busiest days.
Environmentalists have said the event will give the UK a chance to set the tone for the planet’s future.
Scotland’s justice secretary Humza Yousaf has previously insisted the UK government should fund the entire security provision, but the issue has not yet been settled.
A spokeswoman for the Scottish Government said: “Scotland looks forward to welcoming the United Nations delegates and participants from around the world later this year.
“Scotland is recognised internationally for its strong track record at hosting major international events and we are working collaboratively with the UK government, Glasgow City Council and other partners to ensure the conference is a success.
“While the UK government has committed to cover core costs, Scottish ministers expect that all costs associated with COP26 will be borne by the UK government. This includes funding for police, fire and ambulance services to both prepare for and deliver a safe, secure and successful event.
“We continue to push the UK government on the lack of clarity on this key issue.”
In September – when Glasgow was announced as the host city for the summit –Police Scotland suggested costs to the force would be in the “tens of millions”, while October estimates placed the cost at £100 million.
It is not clear what has caused the increase in expected costs, but the latest estimate is based on events such as the Nato Summit in Wales in 2014.
The Scottish Conservatives say “everything” must be done to ensure the success of Cop26.
Shadow environment secretary Maurice Golden said: “Of course the policing and security element will be crucial, and extremely expensive. That’s why both the UK and Scottish governments must put their heads together to ensure the costs are covered, and we aren’t stripping money out of an already hard-up Police Scotland.”
Liam McArthur, justice spokesman for the Scottish Liberal Democrats, said: “This will be an immensely complex operation but I have full faith that police officers and staff will rise to the challenge.”
“The UK and Scottish government need to reach an agreement and ensure that Police Scotland, whose finances are already in a mess as a result of the SNP’s botched centralisation, are not left out of pocket as a result of the additional demands placed on them during this prestigious event.”
Mary Church, head of campaigns at Friends of the Earth Scotland, stressed the importance of the meeting justifies the financial and environmental impacts.
“The climate emergency poses an existential threat to humanity,” she said.
“By its very nature, climate change knows no borders and is an inherently political issue that must be dealt with at the international level. That inevitably involves security costs and some flights.
“It is vital that civil society and particularly peoples’ movements on the frontline of the climate crisis have a strong voice at the summit to shift the balance of power away from big polluters.”
The report also outlines plans for police officers from other forces to be sent to Scotland to aid the force in what is described as “undoubtedly the largest mass mobilisation of police officers in the UK”, adding that it would present “extensive logistical challenges”.
Scottish Labour justice spokesman James Kelly said: “Early preparation to ensure adequate security at Cop26 is essential.
“Any assessment needs to have a clear definition of resources required to police the conference. There also needs to be early discussion between Scottish and UK governments to reach agreement on responsibilities and costs.”
The Scottish Event Campus will play host to the event, being handed over to the United Nations for the duration of the summit, which runs from 9 to 19 November.