The unwelcome scenario of a nuclear-powered submarine aground in full public view was compounded after it was revealed that the Emergency Towing Vessel sent to assist the stricken HMS Astute caused further damage.

The Maritime and Coastguard Agency-operated Anglian Prince collided with the submarine as it was hauled off an Isle of Skye shingle bank. The coming together buckled the submarine’s starboard foreplane. The MoD admitted the grounding had also caused minor damage to the rudder.

With no spare replacement items readily available, the components required to carry out repairs as quickly as possible will have to be cannibalised from vessels further down the production line, in this case from the third hull, Artful, which is due for launch in 2012.

The repairs were carried out at Faslane, where the sub was lifted out of the water for inspection. The full extent of the damage and the cost of repairs have not yet been revealed, nor has the outcome of an inquiry into the incident.