US will not handover JSF source code to the UK

orbitalia writes: The UK is heavily involved in the JSF (Joint Strike Fighter program) but has recently considered abandoning the project because the US refuses to share the source code. The UK intended to purchase $120 billion dollars worth of aircraft to operate on two new aircraft carriers, but is now seriously considering Plan 'B' which is probably to develop the Eurofighter Typhoon further. Should the US just hand over the source?