The revelations are a huge embarrassment for the Joint Strike Fighter project, which has so far cost the UK taxpayer £999 million, and mean the four aircraft ready for the UK cannot fly from the Eglin base in America.
The JSFs, which have stealth capability and will eventually fly from the Queen Elizabeth- class aircraft carriers, are being developed by Lockheed Martin and BAE systems for a group of countries including the US, UK, Turkey and Italy, but have been beset with problems.
In written answers to the SNP’s Westminster leader and defence spokesman Angus Robertson, defence minister Philip Dunne admitted there have been four fires on JSFs, with the latest happening on 23 June.
According to Mr Dunne, the first fire was within the integrated power pack and was due to an internal valve failure. Ground personnel extinguished the fire, and “a minor design change” was made.
He said the second fire was a result of a hydraulic fluid leak on to a brake assembly following landing.
Mr Dunne added: “Ground personnel extinguished the fire which resulted in minor aircraft damage.”
The third fire was due to a hot brake condition after landing which was also extinguished by ground personnel and resulted in the replacement of the wheel and tyre assembly. He said the fourth fire is still being investigated and while flying began again in the US on 16 July, the British planes cannot come over until the results are known.
He noted that all the fires took place on planes which have conventional landing and take- off systems rather than the UK’s B-variant, which has a jump jet system.
The planes were meant to make their first public appearance in the UK at the Royal International Air Tattoo at RAF Fairford in Gloucestershire but Mr Dunne said the plane will not now arrive before 2015.
He confirmed a flight restriction of 25 nautical miles has been placed on all variants of the JSF “until associated design tests have been successfully completed”.
Mr Dunne insisted that further tests were part of the process in getting the JSFs ready to come into service in 2018 as planned.
He said: “The aim of the development test phase is to reveal issues through testing so that solutions can be developed in order to deliver a capable aircraft to the armed forces.”
But opponents said the fires and associated safety risks were concerning.
Mr Robertson said: “Eight years after its first flight and a billion pounds later it is still in testing, the RAF only has three jets to show for it, and they are all currently grounded.”
A spokesman for Lockheed Martin said he was unable to provide further details.