Russia poses the greatest nuclear risk to the UK, a report has revealed, released on the day that parliament is debating whether to replace the Trident nuclear deterrent.
The study by the Royal United Services Institute (RUSI) also points out that China is the next most nuclear-capable country, while India, Pakistan and North Korea all have nuclear programmes that could possess the capability in the future to pose a risk to the UK.
The report comes as parliament discusses on Monday (18 July) whether to replace the current Vanguard Class of nuclear weapons submarines with four new boats, in a programme that would cost more than £31bn ($41bn).
The authors, Professor Malcolm Chalmers and Cristina Varriale, say the risk of an attack has been made more likely due to the deterioration in relations between Nato and Moscow and that Russia is "the primary source of potential nuclear risk to the UK, and will continue to be so for the foreseeable future".
The report states: "As recent events have made clear, Russia and the Western states continue to have fundamentally different concepts of European order, which in turn increases the potential for misunderstanding and conflict.
"As a result of the UK's longstanding Nato treaty obligations, as well as its growing commitment of capabilities to the defence of exposed states in Eastern Europe, the UK is likely to be involved militarily should Russia miscalculate and attack a Nato member state.
"The possibility for conflict with Russia could also arise as a result of disputed strategic interests outside Europe, for example in Syria," the report said.
UK Prime Minister Theresa May has said it would be a "gross irresponsibility" for the country to abandon its nuclear weapons.
It is an issue which has split the Labour Party, whose leader Jeremy Corbyn opposes renewal although the party's MPs will get a free vote, meanwhile all but one of the Scottish National Party's MPs is expected to oppose its renewal.
The UK has four Trident submarines of which one is always armed and at sea. Its aim is to stop a nuclear attack on the UK, whereby even if its defences were destroyed, the 150m-long submarine can launch a retaliatory strike.
The RUSI paper describes how China is the only other potentially hostile power which could attack the UK with nuclear weapons, although at present the risk was limited.
This may change however "if the extent of UK security commitments in the Asia-Pacific region increases, alongside a further deterioration in relations between the US and China", the report added.