SNP activists are preparing to quiz two of their senior MPs on whether the party should continue to support an independent Scotland being a member of the defence alliance Nato.

Stephen Gethins, a member of the party’s Westminster foreign affairs team, and Kirsten Oswald, its armed forces spokeswoman, are to be pressed on the policy, controversially adopted four years ago and which led to three MSPs quitting the party.

The subject is due to be raised during a private question and answer session at the annual conference of the SNP’s CND group in Glasgow which is expected to be attended by between 50 and 100 activists.

“I understand the Q&A will give members an opportunity to ask the MPs for their thoughts on the Nato policy,” one insider due to be at the meeting told The National.

“I’m sure if you were to take a straw poll of members who will be going along there would be very few who would think being pro-Nato was a good thing. I’m certain members will be asking Kirsten Oswald and Stephen Gethins about Nato.”

The SNP voted to ditch their 30-year policy of opposition to Nato at their annual conference in October 2012, backing a resolution put forward by Angus Robertson, the party’s Westminster leader.

But the move – which was supported by 426 votes to 332 – was controversial as Nato backs the use of nuclear weapons while the SNP have long been opposed to them, campaigning against the renewal of the Trident weapons system on the Clyde.

Robertson told the Perth conference that the fresh approach was developed following discussions with other countries and was dependent on Trident nuclear weapons being removed from Scotland and refusal to host nuclear weapons in the future.

Speaking against the policy change, the then SNP Highlands and Islands MSP John Finnie – who subsequently quit the party and is now a Green MSP – said if the party voted to back Nato in an independent Scotland then it would not get rid of Trident nuclear weapons from Scottish shores.

But the party’s then leader and first minister Alex Salmond said he believed it was “perfectly feasible” to join Nato while maintaining an anti-nuclear stance. Ahead of the conference debate he pointed out that 26 out of the 29 countries in Nato did not have nuclear weapons.

Last night, the insider said that since the policy change in October 2012, the party’s grassroots had moved more to the left following the large influx of members since the independence referendum in September 2014.

He added: “A key plank of our defence policy is the removal of Trident. So therefore we have to develop a strategy to have it removed. The question is ‘is it easier to remove Trident as a member of Nato, or not as a member of Nato?’.”

Speaking ahead of the SNP CND conference, Patrick Grady, SNP MP for Glasgow North, said: “The SNP’s vision of a nuclear-free Scotland is a key plank in our case for independence – and a statement of the role we can play in bringing about a more just and peaceful world. SNP CND, and this conference in particular, provide space to explore exactly what that means in the light of recent events including the Brexit decision and vote for Trident renewal – both decisions opposed by people and parliamentarians in Scotland.”

Bill Ramsay, convener SNP CND, added: “One of the key roles of SNP CND is to provide a direct link between SNP members and SNP parliamentarians. Our conference will allow SNP members a unique opportunity to discuss the post-Brexit context as it relates to SNP foreign and defence policy, not only among themselves but with representatives of the SNP’s Westminster team.”

Asked if the Nato policy would be discussed, he said: “Of course. Indeed it would be bizarre if at an SNP CND conference on defence and foreign policy it were not.”

A SNP spokesman said: “The SNP policy on an independent Scotland’s membership of Nato was decided democratically by members at the party’s national conference.”