Why Britain would try to copy an early F-35

Would Britain try to copy an F-35 that appeared in the 1960s?

Yes, despite the technical difficulty, because a domestic version and strong export sales could repay the investment.

An early F-35 would contain advanced technology that Britain could not copy quickly or cheaply. Creating a domestic version could nevertheless bring substantial military and financial advantages. If Britain could sell the resulting aircraft widely, export revenue might repay the demanding development effort. The economics, rather than technical ease, make the attempt plausible.