Something like 99% of cinemas in the UK have it as a condition of their licence that they can only show films which have been certified by the BBFC.
That said, if a local regional authority feels that the certificate granted is not strong enough they can override the BBFC ruling and raise the certification for their area or ban the film all together, this happened with CRASH in Westmister I think it was.
The current ratings are
U - Universal
PG - Parental Guidance
12 - Over 12's only
15 - Over 15's only
18 - Over 18's only
There are some new PG-12 and PG-15 ratings being trialed in some areas. These will work like the normal PG but give parents a better guide as to the films content.
Additionally, Lord of the Rings was recently given a PG certificate but was caveated with an advisory that children under 8 may find the film too intense.
censorship is the worst that brought to film since barbara streinsan . censorship is the thing bringing films like sugar and spice and bring it on and other bad movies more likly to be released in theaters then a soon to be great film like house of a thousand corpses out
"G" General Admission
"PG" Parental Guidance suggested
"PG-13" Some Material unsuitable for children
"R" Restricted, no admitance if your under 17 without a parent
"NC-17" No children under 17, reguardless
"G" General Audiences, all cartoons mostly.
"PG" Parental Guidance suggested, Ella Enchanted.
"PG-13" Some Material unsuitable for children, LotR here is PG-13, the Fellowship I mean.
"AA" Adult accompaniment required. I think the Matrix was this
"R" Restricted, no admitance if your under 17 without a parent, this would be things like Dawn of the Dead, however theaters vary with their ratings here
The wierd thing about the UK system is this... lets say I'm fifteen.... I can go into the video shop, and rent a 15 certificate film, or a 12A certificate (or PG12 depending on where you are in the country...) but I can't rent a PG without an adult's permission... this means I could borrow, for instance, "Pitch Black" or "Jurassic park III" but not "Shrek..." or "Gundam Wing..." bizarre, huh....