I think it would cost an insane amount of money to put the British war manufacturing machine back into service. It would take at least 20 years to get up to a realistic and 'current' level of design and consistency. And there would also be a distinct lack of designers or 'boffins'. Our schooling system no longer creates cutting edge engineers and designers, it churns out 'I know my rights' and baby making machines.
And even then we would still need to rely on foreign powers for the raw materials etc.
Bleak.....