I thought my '77 Grand Prix (s/n Nottingham May '76) with its BSC/ISO 24 tpi BB was something new when I made the first BB swap.
I recently moved an SKF BB from that bike to a '74 International.
At some point in the 70s all the Raleigh Sport-touring bikes went to BSC/ISO threading and it may have been the 1977 model for Grand Prix and Record, which is also the transition to cotterless crank.
I've also heard that any Raleigh with a cottered crank has the 26 tpi Raleigh threading (stated by Sheldon) and at some point it was only the rod-brake roadsters with 26 tpi. But that seems like a lot of trouble in one factory, to be threading essentially the same BB shells and using the same cups with different threads.
the '77 Grand Prix had this same adjusting cup in 24 tpi
quoting sheldon again here, this may be the correct answer
Generally speaking, Raleighs that use cottered cranks have Raleigh 26 TPI threading for both the bottom bracket and the headset. These include all Nottingham-built bicycles sold with a coaster brake or internal-gear hub, as well as lower-priced derailer-equipped models up through the Super Course, which had a frame of plain-gauge Reynolds 531 tubing. Although the diameters are the same as B.S.C., the different thread pitch makes the parts incompatible. This article will provide strategies for getting around this problem.