The catalog number is usually etched (by hand or stamped) in the run out grooves. You can use that to figure out what you have. At the link below, in the discography section, you'll find all the catalog numbers for all releases in all countries (well most, I might be missing a few Bora-Bora, Mongolia or Madagascar pressings...)
If you think you have mostly UK pressings, you can narrow it down quickly: the ROUGH numbers are albums and the RTT numbers are 12" singles.
There are a few instances where you have to be careful. The Meat Is Murder live EP test pressings have the same catalog number as the "That Joke Isn't Funny Anymore" 12". The "Reel Around The Fountain" 7" tp share its number with the "This Charming Man" 7" and some of the "Shoplifters Of The World Unite" test pressings might actually have "You Just Haven't Earned It Yet Baby". You then have to look at the 2-1-U portion of the number to figure out those subtleties.
Stephane