THE SNP leadership last night paved the way for a major showdown with many rank and file members by proposing an end to the party's long-standing hostility to an independent Scotland becoming a member of the Nato nuclear alliance.

The proposed change, to be decided on at the annual conference in Perth, would be "subject to agreement on withdrawal of Trident from Scotland".

SNP critics seized on the potential U-turn, saying it was evidence that defence thinking within the pro-independence campaign led by leader Alex Salmond was "confused at best and negligent at worst".

Nato will be one of the most contentious issues to be debated at October's event, given that a string of Nationalist politicians have, in the past, voiced opposition to an alliance based upon the possible use of nuclear weapons.

The resolution for change is being proposed by Angus Robertson, the party's leader at Westminster and its spokesman on defence, on the basis of an independent Scotland's security responsibilities and obligations.

He said it followed a detailed review, which had included opinions from SNP members as well as outside experts.

Mr Robertson called the proposed resolution the party's "first significant defence policy update in 10 years, which at its heart prepares for better defence decision-making in Scotland".

At present, SNP policy favours co-operation with international alliances, such as Nato, through the Partnership for Peace programme; a similar position to countries like Sweden and Austria.

However, the leadership's resolution says: "The SNP wishes Scotland to fulfil its Treaty obligations with Nato.

"An SNP Government will maintain Nato membership subject to an agreement that Scotland will not host nuclear weapons and Nato continues to respect the right of members to only take part in UN-sanctioned operations."

Failure to secure such an agreement would mean an independent Scotland would work with Nato through the Partnership for Peace programme.

The Nato resolution will form part of a wider foreign, security and defence policy update, which will include a financial commitment of £2.5 billion for defence and security – equating to 1.7% of total Scottish GDP – and a proposal for 15,000 regular armed forces personnel, said to be an increase of 4000 on current levels.

"These proposals will deliver an increase of service personnel in Scotland, restore and protect Scottish units and bases as well as address significant UK capability gaps," said Mr Robertson.

"As a northern European nation, we have domestic and international security responsibilities and obligations including mutual defence.

"We can deliver on these with properly funded conventional capabilities and without the obscenity of Trident weapons of mass destruction."

He added: "With agreement on the withdrawal of Trident and retaining the important role of the UN, Scotland can continue working with neighbours and allies within Nato."

However, the SNP's political opponents said the proposed policy showed the pro-independence campaign was rattled.

Margaret Curran, the Shadow Secretary of State for Scotland, said: "Today's rushed plans for defending Scotland are confused at best and negligent at worst.

"Scotland's defence policy should be determined by the facts and evidence, not dreamt up by Angus Robertson on the back of an envelope. This is yet more spin and speculation from the SNP as they struggle to answer questions about Scotland's future. They haven't come up with the answers Scots are looking for, and now they're beginning to realise it."

Sir Menzies Campbell, the former LibDem leader, told The Herald: "For all the time I have been in Parliament, the SNP has been vehemently opposed to membership of Nato. This policy, if approved, does not make sense. It is based on a doubtful assumption Scotland would automatically inherit all of the Treaty obligations entered into by the UK.

"It's hardly likely that Nato, which acts by unanimity, would accept Scotland on such conditions."

He added: "An independent Scotland, on these assumptions, would want the shelter of a nuclear umbrella but without the responsibility."

Ruth Davidson, the Scottish Conservative leader, described the Nato resolution as "staggering", coming as it did from a party "so furiously against the concept of nuclear deterrent".

She added: "Much like its misguided stance on the EU, the SNP seems to think an independent Scotland would be waved through to join Nato automatically if they reverse their decades-long opposition to the Alliance. They are making it up as they go along."