MSPs John Finnie and Jean Urquhart quit SNP over Nato policy
Highland MSPs John Finnie and Jean Urquhart have resigned from the SNP over the party's decision to end its long-standing opposition to Nato.
The pair described the decision as "heart-wrenching" and said they would continue to sit as independent MSPs with no official party affiliation.
Party leader Alex Salmond said he was saddened by the resignations.
The SNP now has a majority of one at Holyrood, although the MSPs said they would support most party policy.
The change of stance on Nato membership was approved at the party's conference in Perth on Friday by 426 votes to 332.
The policy was opposed by several MSPs and rank and file members, including Mr Finnie and Ms Urquhart.
Frankly, much of the argument for Nato within the SNP rested on a pragmatic calculation that most voters favoured membership.
Mr Finnie and Ms Urquhart have concluded that this is a pragmatic compromise too far.
They will argue that their decision is driven by honourable principle - which many, notably in the Greens, will applaud.
This will subside to some extent as other issues arise, but right now Mr Salmond may feel like offering advice to his colleagues, borrowed from an earlier party leader: "Damn your principles. Stick to your party."
The SNP's stance for the last 30 years has been to oppose Nato, the defence alliance involving the US, UK and other countries.
However, Angus Robertson MP put forward a resolution saying an independent Scotland should become a member of the pro-nuclear weapons organisation.
He told the conference that the fresh approach was dependent on Trident nuclear weapons - which are currently based at Faslane Naval base on the Clyde - being removed from Scotland and on Scotland's refusal to host nuclear weapons in the future.
Mr Finnie and Ms Urquhart, both former Highland councillors, opposed the change of policy.
A member of the SNP since he was 16, Mr Finnie said: "I cannot continue to belong to a party that quite rightly does not wish to hold nuclear weapons on its soil, but wants to join a first strike nuclear alliance.
"Although I envisage that I will continue to share common ground with the SNP on many issues, I cannot in good conscience continue to take the party whip."
Ms Urquhart, who has been a supporter of independence for 25 years and a member of anti-nuclear weapons movement CND for 35 years, added: "The issue of nuclear disarmament and removing Trident from Scotland's waters is a red line issue for me, and I could not remain committed to a party that has committed itself to retaining membership of Nato.
Last Friday's SNP debate on whether to support Nato membership for an independent Scotland was surprising in several ways.
Not least was its rarity in the normally tightly-controlled confines of a modern party conference.
The language was more passionate and direct than usual too.
Normally, strong words from conference podiums is aimed at opposite parties not colleagues.
But on Friday we heard claims of hypocrisy and immorality aimed at the leadership for abandoning decades of opposition to Nato membership and replacing it with a new position which rejects nuclear weapons on Scottish soil but shelters under the membership of the nuclear alliance that is Nato.
Supporters of a pro-Nato policy, like Alyn Smith MEP, were direct too.
He said rejecting the alliance would show the party weren't ready for the "big league".
What wasn't surprising was the passion the subject caused.
Opposition to nuclear weapons is one of the core principles of the modern SNP - so core that two MSPs can no longer bear to stay in the party if its policy is pro-Nato.
But the leadership believe they needed this debate to give them a credible defence policy ahead of the independence referendum.
If being pro-Nato helps secure a yes vote in 2014, they may judge today's loss of two MSPs to be worth it.
"We are both steadfast in our belief that Scotland should be an independent country, and will actively and positively campaign for a Yes vote in 2014.
"We believe in an independent Scotland, not a Nato-dependent Scotland."
Mr Salmond said the pair had been excellent servants to the SNP and thanked them for their "tireless efforts".
He said: "I'm saddened that Jean and John have decided to resign from the party.
"We had an excellent and democratic debate at party conference last Friday, and agreed a policy of reaffirming our opposition to nuclear weapons as a non-nuclear member of the Nato alliance - a position that will be accepted by the party as a whole."
Mr Salmond added: "Jean and John have indicated to me that they will continue to support the government from the back benches, and I welcome that."
Dave Thompson, SNP MSP for Skye, Lochaber and Badenoch, also opposed the change of policy - but said he was disappointed by his colleagues' resignations.
He said: "I've got huge respect for both John and Jean, who are committed Nationalists.
"I'm disappointed they've chosen to resign from the SNP over this issue. It is an issue people hold very strong views about.
"Personally I was against the change in our policy and campaigned very strongly against it, but I've got no intention personally of leaving the SNP. I'm going to stick in there and try to secure and build on the guarantees we were given during the debate."
The resignations leave the SNP with 65 MSPs, which still gives the party a majority in the Scottish Parliament.
A total of 69 SNP MSPs were elected in May 2011, but the choice of Tricia Marwick as presiding officer meant reduced the number to 68.
Dunfermline MSP Bill Walker was expelled from the party in April following allegations of domestic abuse.