The Royal Navy’s fleet already includes adapted commercial ships such as HMS Protector

The Royal Navy is to convert two passenger ferries or cargo vessels into warships as part of a thrifty modernisation plan, the defence secretary has announced.

Gavin Williamson also disclosed yesterday that he planned to buy and adapt off-the-shelf drones to create a swarm fleet that could interact with the military’s highly sophisticated F-35 multirole stealth fighter jets.

The new swarm squadrons would be “capable of confusing the enemy and overwhelming their air defences”, he said. Scores of unmanned aircraft would be used to target hostile states’ radar.

The decision to buy and adapt off-the-shelf models means that the programme would be quicker and cheaper than procuring bespoke versions. The drone programme is expected to cost £7 million and is due for completion by the