A FIBREGLASS MODEL in battleship grey was one of the unlikely stars of last week’s Farnborough air show. While casual visitors gawped at the fighters roaring overhead, or oohed at the sleek, sinister shapes of the latest unmanned stealth aircraft from America, those in the know trudged up through the corporate boxes to scrutinise the unprepossessing mock-up.

It was a model of the Joint Strike Fighter (JSF) — or F-35, to give it its American service name — a combat aircraft that will not go into production for another four years and is unlikely to enter service in Britain until 2011 at the earliest.

It may be some time before it fires a shot in anger, but the JSF has already assumed monumental importance for the future of Britain’s defence industry. Such are the tensions over its development and manufacture that a rift is emerging at the top level of the transatlantic defence alliance between Britain and America.

At issue is the Pentagon’s perceived reluctance to share the sensitive defence technology that would allow Britain to play a bigger part in the programme. In particular, Britain wants access to the software codes that would allow it to repair and upgrade the aircraft, so it can maintain an independent fleet without recourse to America.

Mike Turner, chief executive of BAE Systems, Britain’s largest defence contractor and a member of the Lockheed Martin-led consortium building the aircraft, is forthright.

“It is vitally important as a nation that we are self-capable when it comes to JSF. We need the software codes to have the capability to fit new weapons on the aircraft — otherwise we will have to join a queue with everyone else to have the job done in America,” he said.

British politicians have now taken up the cudgels. Lord Bach, the defence procurement minister, has visited the Pentagon to voice his displeasure at the slow pace of technology transfer, while at Farnborough his boss, Geoff Hoon, the defence secretary, confirmed he had written to Donald Rumsfeld, his American counterpart.

Hoon would not disclose the contents of his letter, but industry sources said he had reminded Rumsfeld that the two nations had signed an outline agreement on defence technology co-operation two years earlier, but that little progress appeared to have been made since then.

Turner and the politicians are playing for high stakes commercially as well as strategically. The JSF will become probably the largest military programme in history. Sales of the aircraft are expected to bring in between $200 billion and $400 billion (£108 billion- £217 billion), with service and support estimated to rake in four times that sum over the plane’s life.

It will become the backbone of America’s air force, marine corps and navy for the next 40 years, replacing several types of existing aircraft, from Harrier jump jets to out-and-out fighters such as the F-16.

The plane’s promised versatility gives it enormous export potential, especially as America has decided to make its design and construction an international collaborative effort, with 11 partner nations having already signed up. Top of the heap is Britain, which will buy up to 150, and has paid £1.4 billion to be the sole “tier one” partner in the programme.

But the partner nations are not entirely happy with the way America has handled the project, claiming that stateside firms have been handed the lion’s share of the work, and that the Pentagon’s sensitivity to the export of defence technology has stymied plans for their involvement.

Norway, which has invested $125m, has threatened to withdraw its involvement unless more work is forthcoming, while Italy has also complained about America’s reluctance to share defence technology.

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