The UK is being urged to break away from , and on the position on a UN resolution focused on a nuclear conflict panel.
The possibility of creating a panel of scientific experts to examine the potential international impact of will be discussed on Friday by a UN general assembly committee.
Non-proliferation groups called on the UK to make a last minute U-turn on its expected position, which is to vote against the resolution - alongside France, Russia and North Korea.
Arms control advocates expressed disappointment in for not showing signs of changing its position.
Patricia Lewis, head of the international security programme at the Chatham House thinktank, said, as reported by the : "People naively thought that, with a Labour government, you would see a shift away from this kind of weird line that the UK has taken on this particular type of thing.
"Maybe this is the Labour party trying to be more Catholic than the pope when it comes to nuclear weapons, but why not vote with the US, and abstain?"
US and China are predicted to abstain according to diplomats involved, but the UK, France, and North Korea indicated they were likely to vote against.
The UN panel would be made up of 21 scientific experts and would examine "the physical effects and societal consequences of a nuclear war on a local, regional and planetary scale".
Scientists say the work would be essential due to the changed landscape of nuclear conflict since the last study in 1988.
Previously it was expected the world would face a "nuclear winter" only if there were a major nuclear conflict between global superpowers, but it's now predicted a nuclear exchange between regional adversaries could do so.
Some believe the UK position to vote against the panel could be down to a desire to build relationships with France.
Physicist and co-director of Princeton University's programme on science and global security, Zia Mian, said: "I think this is building bridges with the French. The French don't want to be alone with the Russians and the North Koreans and whatnot in voting no."
The resolution was drafted by Ireland and New Zealand and is expected to be overwhelmingly approved by the committee and then later by the full assembly.
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