A few links
http://www.welsh8ball.com/
http://arseweb.com/pool/r.html
General differences between UK and US 8-ball
There are also various differences from other sets of (eg US) pool rules which are common to all 3 codes...
The balls and the table
Since American pool game such as 9-ball and straight pool, requiring spots (solids) and stripes are really only ever played on American-style tables in dedicated clubs, these kinds of balls have been almost completely phased out from UK 8-ball tables. When playing on a UK table, you will almost always find that there are 7 solid red balls and 7 yellows, plus the black which retains its white spot and number and is still called the 8-ball.
In EPA and BAPTO rules, the balls are racked like this. In World Rules there is a slight difference (swap the balls 2nd and 3rd from the right in the bottom row)
The game is played with 2" object balls. Usually the cue-ball is slightly smaller (1 7/8"), although very rarely (when not paying per frame) one comes across sets where the cue ball is the same size as the others).
Tables vary in size. The table should be twice as long as it is wide, and can be 6ft, 7ft, or 8ft long.
The jaws of the pockets are more rounded than on a US table. This tends to mean that potting a ball into a corner pocket down the cushion is much harder. Potting into side pockets, from a narrow angle, is however much more feasible than on an American table.
Legal shots
Jump shots are illegal (defined as the cue ball jumping over any part of any ball before making contact with any object ball). In World Rules, a Jump Shot is a "serious foul" ie doing it twice leads to loss of frame!
In most situations a player must play away from a touching ball (which if it is a ball "on", will be deemed to have been hit). But see above for EPA and World Rules exceptions)
There is no concept of calling shots whatsoever. Occasionally one comes across people who like to play call pocket on the black, but this does not appear in any official rules.
There is thus no concept of "calling a safety". If a ball is potted on a legal shot, the player at the table is always obliged to play again.
The US requirement that a ball hit a cushion if nothing goes in only appears in World Rules (see "Hitting a cushion" above). In the other 2 codes, simply rolling up to your own ball to leave one's opponent snookered behind it is a common tactic. In World Rules, rolling up to your opponent's ball is a more common tactic! (because they won't be able to move the cue ball or play a free ball, so will often have to "waste" their first visit in playing the cue ball to somewhere more useful)
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"House Rules" (local variations)
You'll find some pubs, people, and even a few of the smaller local leagues play "house rules" which vary slightly from the published sets. Some of the more common variations include:
Call pocket on the black (often you have to stick to the pocket once it's been called)
Push shots allowed (see "Push shots & touching balls" above).
Can never move the white after a foul. This is how it used to be played years ago.
Can only move the white after a foul if you're snookered (this is an old variant from EPA and BAPTO rules, when moving the white after a foul was first brought in, this was how it worked). Note that there are different definitions of "snookered". It can mean
"can't see any part of any ball 'on'"
(cf World Rules 'Total Snooker' ), or
"can't see to play 'thinnest possible cut' on any ball 'on'"
(cf World Rules 'foul snooker/f ree ball') or
"can't see to play full-ball shot on any ball 'on"
(once upon a time official BAPTO rules said you could only move the white after a foul if snookered in this sense, still played in some local leagues: every variant that there ever was is still played in some local league somewhere!)
You only ever have one shot on the black. It's surprising how many people think this variant makes sense. They suggest that having 2 shots on the black makes it too easy for the person who's on the black. Actually their variant makes it far too easy for the person who's NOT on the black.
Some places have extremely non-standard rules. One of the oldest is the Bridlington rule set used in the East Riding of Yorkshire. They play call-pocket on the black, and push shots are allowed.
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Pool rules links
EPA: English Pool Association (governing body for World Rules and formerly old EPA rules)
EUKPF: European & UK Pool Federation (governing body for Federation rules)
BAPTO: British Association of Pool Table Operators NB this site is usually out of date, see EUKPF site for more up-to-date info
BCA: Billiard Congress of America. NB the EPA "World Rules" described above are NOT the same as the BCA's "World Standardised 8-ball rules".
My Killer page
UK8ball forums for discussion of the various rules: technical and tactical queries regarding both individual rule sets and comparisons between rule sets.