The Defence Secretary has been urged to intervene to end a strike at a Beith defence depot after suggesting the missiles built there could win the war for Ukraine.

The SNP wrote to Grant Shapps on Monday calling on him to resolve the dispute as another two-week walkout begins at the munitions plant.

In his letter, the party’s defence spokesman at Westminster Martin Docherty-Hughes accused the Ministry of Defence (MoD) of failing to engage with workers to end the pay dispute which has led to a series of strikes over the summer.

Andy Start, chief executive of Defence Equipment and Support (DE&S), part of the MoD, says he cannot talk to GMB Scotland, representing the striking workers, until next month in Bristol.

Mr Docherty-Hughes urged the Defence Secretary to intervene and ensure the executive team travel to Beith as a matter of urgency.

He said management had so far shown a “lack of urgency and a callous attitude” to the striking workers, who had postponed their action in good faith to allow talks at conciliation service Acas only for no offer to be made.

Mr Docherty-Hughes said the workers deserved recognition, respect and fair wages, adding: “Travelling to Beith would be an important gesture to rebuild trust.

“I am writing to ask you to bring some urgency to the resolution of this dispute and encourage the DE&S chief executive to travel to North Ayrshire ahead of this scheduled meeting in a month’s time.”

The striking non-craft workers at Beith, who have won cross-party support of Ayrshire MPs and MSPs at Holyrood, provide logistical support to the craft workers, who assemble the weapons.

However, there is a widening gap between their pay and bonuses and that of their non-craft colleagues, who can earn £21,000 while taking responsibility for the transport of multi-million pound missiles, including, according to publicly-available documents, Storm Shadow missiles being sent to Ukraine.

On Monday at the Conservative Party conference in Manchester, Mr Shapps said those missiles could change the course of the war: “With weapons like Storm Shadow, everywhere in Russian-occupied Ukraine, is on the front line.

“The war is consuming weapons, ammunition and, yes, people at an appalling rate.

“If Ukrainians are to prevail against the evil assault on their homeland, we must remain steadfast.”

Chris Kennedy, GMB organiser, said the defence secretary’s decision to highlight the importance of Storm Shadow missiles only underlined why he must intervene to resolve the dispute in Beith.

“The importance of our members’ work is not in dispute and the defence secretary is only the latest to emphasise their crucial role supplying our own armed forces and Ukraine’s.

“It is beyond time for a fair offer to be made and this dispute to be resolved.

“We are ready to talk today, we were ready to talk yesterday and we would be ready to talk tomorrow but we cannot talk to ourselves.

“The decision-takers, the people who can actually resolve this dispute, should be in Scotland now. The disregard and disrespect shown to such important workers has gone on long enough.

“Before Grant Shapps leaves Manchester he should be phoning DE&S and telling its management to get back around the table because that is the only place this dispute can end.”

A Ministry of Defence spokesman has said: “These strikes will have no effect on our ability to provide capability to Ukraine.

“Pre-planned contingency measures are being implemented at Defence Munitions (DM) Beith to ensure the continued safe and compliant operation of the site.

“We remain open to dialogue with GMB to discuss the issues raised and work towards resolving them.”