Shipbuilding trade unions are “gravely concerned” that possible delays to the Ministry of Defence’s £4bn ($7.8bn) contract for two new aircraft carriers, revealed by the Financial Times last week, could threaten jobs on the Clyde as soon as October.

The unions are furious that the MoD last month put out to international tender an £800m contract for six vessels – Military Afloat Reach and Sustainability auxiliary ships, or MARS – which they believe could have been used to fill gaps in the workflow of UK yards caused by delays to the aircraft carrier programme.