BiFest is a one-day event celebrating bisexuality, for bisexuals and bi-friendly people. Originating in London, it has now spread to several other UK locations.
Birmingham BiFest will happen on 17 November 2012 at The Nightingale Club; see this Facebook event page for details.
Oxford's third BiFest was at the East Oxford Community Centre last March; see oxford.bifest.org for details. There may be another next year, but nothing has been announced yet.
There was a London BiFest on 23 June 2012, to coincide with World Pride. There will probably be another next year - the site at london.bifest.org will have details when they're available.
Unfortunately, the planned Cambridge BiFest in late October has been cancelled.
A Manchester BiFest is planned fort he second half of 2012 – see manchester.bifest.org for details.
Wales is hosting its third BiFest in Cardiff in spring 2012: details on Facebook here.
Brighton BiFest happened on 7 March 2009. Details of that event are at brighton.bifest.org. There may be another soon, but no definite plans.