9 kg gas bottle size

I own a second-hand motorhome, and recently bought an exchange gas cylinder, only to find it is too big to fit into the hatch. It would appear that what I always thought was a standard dimension item, is not. Does anyone know if the smaller (by about 20mm) bottle is available, or do I have to have mine re-surveyed, and hope that it passes-luckily I did not exchange my out-of-date bottle. Flaming annoying that they change these things on us.