SSSETOWTF
Can you expand on that calculation? The biggest UK-domiciled piece of JSF is part of the airframe - let's say 15 per cent by value of airframe and systems, which may be 35 per cent of the whole deliverable air system. So the VAT on that is one per cent of the value of the complete air system... so to make our money back on 138 aircraft they would have to sell (click click whirr) 13800 jets.
Yes, there are also the ejection seats and other bits, and some of the B propulsion system (but the Bs are never going to be more than 15 per cent of the production run), and some of the F136 if it doesn't get canceled, but a lot of the RR propulsion work is being done in Indianapolis. Likewise, BAE's biggest chunk of the system is in Nashua.