As I understand it, the standard (American) SAE 45 double flare is the same as the "Girling flare". Same thread on the male ends too.
An alternate Brit flare (which I *think* is more widely used on Lockheed brakes) is the "bubble flare", which I believe is more of a bell-shaped single flare. But again, they usually have the same thread on the male-end couplers.
I remember using American lines in a TR3, but it had Girling brake parts.
As Dave says, best bet is to bring in your old lines and match them up carefully.
Note: there are also 37 degree metric lines, but I doubt you'd mix these up with SAE/Girling sizes.