Yes indeed it's a British Canteen, and it looks to be the slightly earlier WW2 pattern.
The service number I believe is from WW2 and is to the RASC (Royal Army Service Corps)
Thanks Gary! Appreciate it very much..
If you look carefully on the shoulder strap and on the waterbottle web cradle, you may be lucky enough and find a manufacturers logo, initials and date stamp if they haven't faded too much.
On the cradle, these are usually on the internal face of the strap with the female part of the press-stud or the top cross piece and on the shoulder strap on the inside face, which in this case is the side that has the letter "L" on it.
The date stamp on the waterbottle itself is usually stamped into the enamelling on the base or one of the shoulders, so the only way of getting to that is to take off/burst the stitching on the cover itself, which I would NOT advise, because you would never be able to refix it properly.
All in all, a nice piece of kit in good overall condition, I LIKE IT, (but, then again, as is fairly common knowledge on the forums, I like everything relating to 37ptn and 44ptn webbing)