ALEX Salmond is facing a growing revolt over plans to drop the SNP's historic opposition to Nato, with at least seven MSPs now throwing their weight behind a campaign to keep the policy.

Two more Nationalists have joined MSP Jamie Hepburn's campaign to ensure the party keeps its long-standing stance that it would leave the alliance after independence.

Another MSP has indicated to The Herald he will make a decision on whether to join the group after speaking to his constituency party.

Yesterday, Nationalist Glasgow list member Bob Doris and Edinburgh Central's Marco Biagi put their names to Mr Hepburn's amendment to a motion by the party's defence spokesman Angus Robertson proposing an independent Scotland would retain Nato membership. Mr Robertson, who is also the party's Westminster leader, adds in the motion – which will be debated at the autumn party conference – that it would be "subject to an agreement that Scotland will not host nuclear weapons".

Mr Biagi said: "I am one of the co-proposers of Jamie Hepburn's amendment. I'm uncomfortable with membership of an alliance where mutual defence is explicitly underpinned by the threat of use of nuclear weapons. The SNP is now the only party where members can be a real part of policy-making through the annual conference."

Glasgow Kelvin MSP Sandra White said: "I fully support the amendment.

"Nato is an umbrella organisation with nuclear weapons and that's the big sticking point. We cannot put ourselves in that position. For me that's the point of no return."

Meanwhile, Glasgow Shettleston MSP John Mason has indicated he is considering joining those opposing the new pro-Nato strategy. He said his local party would be discussing the issue early next week and he would be "very much guided" by it.

Central Scotland MSP John Wilson said he is not backing Mr Hepburn's amendment because it does not go far enough.

In his motion, Mr Hepburn – MSP for Cumbernauld and Kilsyth – states: "As Nato continues to be a nuclear weapons-based alliance, conference resolves the SNP position will continue to be that Scotland should not remain a member of Nato."

It is understood his parliamentary co-proposers now include John Finnie, Ms White, Jean Urquhart, Dave Thompson, Mr Doris, and Mr Biagi. Ms White hopes to speak in the conference debate opposing the leadership's bid to accept Nato membership. She added: "It's a very important issue not just for me, but many in the party. I've had lots of people saying 'well done' for your stance."

It came as around 20 people yesterday attended a protest by the Trident Ploughshares anti-nuclear group outside the SNP headquarters in Edinburgh. They staged a mock death and lay down outside the building to signify the impact of the weapons on human life. Jane Tallents, 54, from Helensburgh, said: "Belgium has nuclear weapons on its soil and its government has asked for them to be removed, but its requests are not being heeded because it is signed up to Nato and is stuck with them."

She said Mr Salmond would be "completely unprincipled" if he supported the new pro-Nato stance.

Bill Ramsay, organiser of the SNP

CND party grouping, said a significant number of branches and affiliated organisations, including the SNP trade union group and the Glasgow Southside Central branch, were opposing the leadership motion.

He said Mr Robertson would also face opposition from SNP trade unionists over his detailed proposals for a conventionally armed Scottish Defence Force.

Mr Ramsay added: "The unamended motion would allow for a Nato force structure which would enable Scotland to play the sort of role currently undertaken by Denmark, which, although a small country, is an enthusiastic bit player in the USA's constant expeditionary warfare mode. We would rather Scotland uses its independence to opt out of these wasteful, expensive expeditionary wars which undermine rather than enhance our security."

Green MSP Patrick Harvie said: "Greens remain committed to ending Scotland's participation in an outdated nuclear alliance."

Green activists are threatening to turn up at the SNP conference in Perth in October in a bid to persuade Nationalists to switch sides to a "genuine anti-nuclear, pro-independence party".

An SNP spokesman said: "The SNP has a cast-iron commitment to rid Scotland of nuclear weapons. Given the continued presence of Trident nuclear weapons in Scotland – against the wishes of her Parliament and people – independence is the only constitutional option which makes this possible.

"SNP members have the democratic opportunity to make their views on Nato membership clear at the annual conference in October, where we expect to have an excellent debate."