But, in May this year, it performed a U-turn, saying it would revert to the F35-B, as costs had increased.

BBC: Joint Strike Fighter planes (file pic)

It says the US - which is leading the F35-B project - is likely to cancel its orders, as Washington struggles with a government debt crisis.

BBC: Joint Strike Fighter planes (file pic)

Mr Hammond insisted the risks associated with the F35-B were "dramatically different now" to what they were in 2010 when there was a possibility it would be cancelled due to technical problems.

BBC: Government in ?100m U-turn over F35-B fighter planes