The jets are due to come into service in eight years time
Defence chiefs have admitted "concerns" over a £5 billion order for fighter jets that are too heavy to take off from warships.
The US Joint Strike Fighters are due to replace Britain's ageing Harrier fleet.
The jets, which cost around £35m each are said to be 3,300lbs (1,500kg) overweight.
The MoD said the plane's engine was heavier than envisaged, but added problems normally occurred in the early stages of complex programmes.
From our perspective, these problems do not undermine the programme or our choice of aircraft
Ministry of Defence spokeswoman
Britain has agreed to buy 150 of the new jets. They are due to come into service by 2012.
The Lockheed Martin planes are 45ft long and 30ft wide.
The fighter jets are said to have greater speed and stealth with which to penetrate the most sophisticated surface-to-air missile defences.
But though the aircraft's engine is widely accepted as the most advanced of its kind, it is far heavier than expected.
If the weight problem is not resolved, the jets will be unable to achieve the vertical take-offs that are the trademark of the Harrier Jump Jet.
'Problem will be solved'
Britain is building two new aircraft carriers for the Royal Navy - but the runways will be too short for the jets to take off normally, newspapers have reported.
A spokeswoman for the MoD said: "The weight problem is a concern but problems like this occur in the early stages of complex programmes.
"The projects are being carefully co-ordinated and the problem will be solved in time for the jets to come into service in 2012 as planned.
"From our perspective, these problems do not undermine the programme or our choice of aircraft."
GDB From United Kingdom, joined May 2001, 12947 posts, RR: 79 Reply 2, posted (9 years 6 months 3 weeks 3 days 13 hours ago) and read 2813 times:
It's been well documented that F-35 has some weight issues, however, it (and the Harrier) do not use vertical take off in normal operations, that's what the ski-jump on the ships are for.
And CVF will likely be 3 times the size of the current Invincible Class, (which are too small for F-35).
Vertical take offs are for airshows, forget any kind of range or payload if use it on operations.
It seems the BBC saw something in Hansard, and 'sexed up' the rest, make the story more interesting for the layman.
The last time I heard, STOVL stood for 'Short Take Off/Vertical Landing', everyone except some hacks seem to understand that, F-35B, like the Harrier, are STOVL aircraft.
But yes, LM do have some weight issues to fix.
Still, they picked the right aircraft, the Boeing X-32B contender had to lose undercarriage doors and the inlet to perform vertical take offs, which the X-35B demonstrated successfully.