Just to tidy up the answers above:
6 points within the first two years of holding a licence automatically revokes the licence but it doesn't impose a ban. The driver can re-take their test and, if they pass, get a new licence.
For anyone else, 12 points would normally result in a ban but the courts have discretionary powers and occasionally allow people to continue to drive with 12 or more points.
Points remain valid for 'totting up' purposes for 3 years but can't actually be removed from a licence or a further year. (There are some exceptions, where longer periods apply but they're only relevant for particularly serious driving offences).