Looks like a medic / mountain troop canteen. Not sure about the numbers tho.
Would need a pic of the other side also, to decide whether it is medic or GJ.
If the cup is a gfc 44, then it is most probably a fake (plastic) one....
ESB is a valid maker, never heard of PEI (you probably mean RFI)
and indeed, to determine if it is a GJ or medic canteen we should see the other side
Looks like the belt support hook has come out??
That and there is the broken cap strap that would normally hold the screw lid ( that is why the cap is off another canteen I would guess )
" When you're chewing on life's gristle, don't grumble, give a whistle "