Good news on the inspection.
Late Spitfires and GT6's had dual circuit brakes. They use a GMC226 master cylinder, which are about £80 -
https://www.ebay.co.uk/itm/TRIUMPH-S...wAAOSwY3BZHVw4
From memory I think they have metric pipe unions, there is a version with imperial unions but it's about twice the price so it's cheaper to just change the pipe unions at the master cylinder end of the brake lines.