I've always liked IMR 4320 with this rifle and cartridge. In fact, it's the main powder I use in the .303. As usual, work up from well below 40 grains. Your No. 1 is the weakest of all Lee Enfield actions, so you may max out below the maximum load listed in the book.
Another option is to try to duplicate the old WWI classic military load with the 174. During WWI, DuPont developed a powder called "MR 16", which was actually the precursor of what would eventually be called IMR 3031. They loaded that powder (something like 37.5 grains) with the 174-grain military bullets, and that became the classic .303 military loading. To this day, nearly 100 years later, many people swear by IMR 3031 at something around this charge level with the 174-grain bullet in the .303. I've never tried this load (because I'm very happy with IMR 4320), but I'm sure it would work.