Easy to identify this flat tanker as a New Imperial as it's written prominently on the tank, further than that I am not sure. NI had a rather bafflingly wide model range through the twenties, all with numerical codes. This could be a Model 1, 2 or 3 with perhaps an A, B or C suffix. I'm guessing at a 293 or 346cc motor and a year of arounbd 1925. Any NI experts out there please do chip in.