The UK is carrying out inspections of its stealth fighter fleet and has paused some flying following the crash of a US jet.
Aircraft are being examined to see whether they have a faulty fuel tube after the crash of a US Marine Corps F-35B in September.
The Ministry of Defence said that trials of the F-35 on the Royal Navy's aircraft carrier HMS Queen Elizabeth were continuing.
The RAF and Royal Navy are being equipped with the F-35 Lightning. So far 10 of the aircraft have arrived at Marham, which will be their main land base.
They regularly fly training sorites over Norfolk.
A MoD spokesman said: 'Safety is our paramount concern, therefore the UK has decided to pause some F-35 flying as a precautionary measure while we consider the findings of an ongoing inquiry.
'F-35 flight trials from the aircraft carrier, HMS Queen Elizabeth, are continuing and the programme remains on schedule to provide our armed forces with a game-changing capability.
'We will continue to review the situation as further information becomes available.'
It is understood that some aircraft have already been inspected and have been cleared to return to flight.
Britain has committed to a £9.1 billion programme to buy 48 of the jets by 2025, with a pledge to purchase 138, they will be jointly operated by Royal Air Force and Royal Navy pilots.
The lead manufacturer is US firm Lockheed Martin but across the 3,000 jets being built, 15% of each one is comprised of parts from British companies.
In a statement, the F-35 Joint Programme Office said the US and its international partners had suspended flight operations while a fleet-wide inspection of fuel tubes was conducted.
'If suspect fuel tubes are installed, the part will be removed and replaced. If known good fuel tubes are already installed, then those aircraft will be returned to flight status,' the statement said.
'Inspections are expected to be completed within the next 24 to 48 hours.
'The action to perform the inspection is driven from initial data from the ongoing investigation of the F-35B that crashed in the vicinity of Beaufort, South Carolina on September 28.'
A Lockheed Martin spokesman said: 'We are actively partnering with the Pentagon's F-35 Joint Programme Office, our global customers and (engine manufacturer) Pratt & Whitney to support the resolution of this issue and limit disruption to the fleet.'
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