Admiral Lord Alan West issued the demand to defence chiefs in Whitehall, calling on them to ensure ‘enough’ F-35B are purchased.
The fearsome fighter jets will form the teeth of Britain’s new carrier strike group, flying from aircraft carriers HMS Queen Elizabeth and HMS Prince of Wales.
But Labour peer Lord West, a former security minister, said a government target to buy 138 could be at risk during the Integrated Security, Defence and Foreign Policy Review, set to be unveiled this autumn.
His fears follow reports the Ministry of Defence had discussed buying just 70 of the jets instead of 138 as a ‘minimum credible F-35 fleet’.
Speaking to The News, Lord West said: ‘We need to know what is going to be squeezed. We absolutely need to get sufficient F-35Bs to man up both carriers.
‘We need a minimum of 70 but ideally we need about 90 F-35Bs. We said we’d order 138. But what we mustn’t do is cut the number down to less than 90 because that will not be sufficient for the carriers.
‘The weapon system of the carrier is it’s aircraft. If it doesn’t have any aircraft on it, it doesn’t have a weapons system. So not having the right number of F-35Bs to man up both carriers would be very stupid.’
Whitehall spending watchdog the National Audit Office has previously warned that not enough funding had been made available for sufficient F-35 jets.
In its ‘Carrier Strike – Preparing for deployment’ report, the NAO said: ‘From 2015, its intention has been to buy 138 Lightning II jets, which will sustain carrier strike operations to the 2060s.
‘The department initially ordered 48 jets but has not yet committed to buying any more. In response to wider financial pressures, it will also receive seven of the 48 jets in 2025, a year later than planned,’ the NAO said.
Since 2017, the costs of the F-35 Lightning II project has ballooned by 15 per cent from £9.1bn to £10.5bn.
The first tranche of 48 jets are expected to be acquired by 2025, two years after the expected date to declare full operating capability for carrier strike.
A spokesman for the Ministry of Defence said: ‘Decisions on future F-35 numbers and aircraft variant will ensure the right capability for our armed forces along with value for money. The upcoming integrated review will allow the UK to determine the best variant for future F-35 purchases.’