The UK has a thriving bisexual scene, which does not resemble the gay scene very closely.
The UK gay scene grew out of the illegality of homosexuality - people had to meet up and cruise in secret for fear of repercussions and stigma. As illegality faded, the pubs that catered to the gay scene started to be more visible, and some such pubs in the UK have been gay for more than 50 years.
Bisexuals have always been very prevalent on the UK gay scene, but since the 1980s an additional separate 'bisexual' scene has emerged. Initially coming out of the trade union movement (the first national bisexual conference was organised by trade union activists) the bi scene is less about pubs and clubs and more about social activism. There are no bisexual bars, yet!
The LGBT scene in the UK still contains many bisexuals, not all of whom are out about their bisexuality. There is also a lot of bisexual people in the UK that don't socialise on the LGBT scene, or attend bisexual events.
The largest event in the UK is the National Bisexual Conference & Convention, called for brevity BiCon. Founded in 1984, the event moves around the country, so that each year is accessible for different communities. It is a weekend long residential event, usually held at a university campus outside of term time and regularly attracts more than 250 people.
Throughout the year there are regional events called BiFests which are one day festivals celebrating bisexuality. These are less formally organised than BiCon, and have a focus on people new to the bisexual scene.
At a local level many towns have bisexual groups and almost all universities in the UK have an LGBT society. Since the late 1990s (and with greater frequency since the 2006 Equality Act) a large number of lesbian and gay organisations have come to embrace the power of 'And' by becoming LGBT organisations.
The definitive list of bisexual groups around the UK can be found over at Bi Community News and if you're thinking of starting a new group, we recommend their "A to Z of running a bi group" as an excellent primer.