The submarines will be built under the AUKUS pact – a trilateral security agreement between Australia, the UK and the US, designed to assist Australia in acquiring nuclear-powered submarines.

The pact also includes cooperation on artificial intelligence, quantum technologies, undersea capabilities and electronic warfare.

The UK’s next-generation nuclear-powered attack submarine programme, known as SSN-AUKUS, will see the construction of the largest and most powerful attack submarines the Royal Navy has ever operated, which will replace the Astute class currently in operation.

BAE Systems started early design work in 2021, but the £3.95bn funding will cover development work up to 2028. It will enable the defence firm to move into the detailed design phase of the programme and begin to procure items for its development.

Manufacture is expected to start at the end of the decade with the first SSN-AUKUS boat due to be delivered in the late 2030s.

The award...