The Royal Navy’s ability to operate its two new aircraft carriers may be severely restricted due to a lack of support vessels to keep them supplied, the Whitehall spending watchdog has warned.

The National Audit Office (NAO) said the Navy has just one supply ship able to keep the Carrier Strike force stocked with food and ammunition while on operations.

The NAO also warned the force’s new Crowsnest airborne radar system – which forms a crucial part of its defences – was running 18 months late, further diminishing its capabilities during its first two years.

It said the Ministry of Defence (MoD) had yet to commit the funding required for enough Lightning II fighter jets to sustain the carriers over their expected 50-year operating life.

Meg Hillier, chair of the Commons Public Accounts Committee which follows the work of the NAO, said the Navy was in danger of being left with a “hollowed-out” capability unless the issues were addressed.

The MoD has said it expects to meet its target of declaring an “initial operating capability” for Carrier Strike with a fully-trained Lightning II squadron of up to 12 jets by December 2020, albeit with only a “basic” radar capability.

However, the NAO said it faced a “tight timetable” if it was to achieve its next milestone of developing a “full operating capability” – with two Lighting II squadrons operating from one of the carriers – by 2023.

The MoD has lofty ambitions for the carriers, but hasn’t put its money where its mouth is

It said the MoD had long been aware the lack of support ships would restrict the force’s “operational freedom” but had yet to come up with a solution.

A competition to build three new vessels was scrapped due to concerns about value for money, delaying their introduction by up to three years.

It was now uncertain whether the first of the ships would be ready in time for 2028 when the one existing ship is due to be taken out of service.

At the same time the MoD had failed to developed an airlift capacity to support the force and was relying on ageing Merlin Mk 4 helicopters – which were to supposed to go out of service at the end of 2021 – to ferry people and and equipment to the ships.

The NAO said the delay to Crowsnest – due to failure by a sub contractor, Thales, to meet its commitments – meant the initial contracted capability would not be in place until September 2021, with the full capability delayed to May 2023.

While the MoD had originally planned to acquire 138 Lightning IIs, to sustain Carrier Strike to the 2060s, it has so far only committed to buying 48.

Since 2017, the approved cost of the Lightning II project has risen from £9.1 billion to £10.5 billion, due to capability upgrades, with further increases expected.

The MoD is now planning to review the number of aircraft it needs as part of the Government’s integrated review of security, defence, development and foreign policy.

However, the NAO said any reduction would act as a further constraint on its ability to use the Carrier Strike force.

Overall, it warned the MoD may not have made sufficient provision in future years’ budgets to reflect the full costs of operating the carriers.

Ms Hillier said: “The Ministry of Defence has lofty ambitions for the carriers but hasn’t put its money where its mouth is. Worryingly, it still doesn’t know the full cost of supporting and operating Carrier Strike.

“It must now ensure that the three frontline commands involved sing from the same hymn sheet. Otherwise, the Royal Navy will be stuck with a hollowed-out capability and unable to satisfy expectations.”

A MoD spokesman said: “Carrier Strike is a complex challenge, which relies on a mix of capabilities and platforms. We remain committed to investing in this capability, which demonstrates the UK’s global role.

“Despite the disruptions of Covid-19, the Carrier Strike group is on track for its first operational deployment.”