BiCon is the UK's longest continually running LGBT+ event, having been held at least once a year since 1984..
.. and has been so even before there was no Pride event in London in 2021: the people who attempted to organise one in 1998, following the end of the Pride Trust, failed to do so.
(The next longest running is probably Manchester's pride event, which was first held in 1985.)
To attend a BiCon, ask that year's organisers..
.. and be aware that you will have to pay like any other attendee and abide by the Code of Conduct that will include things like getting specific permission before identifying anyone publicly, or taking photos, videos or audio recordings. Even if you do not use 'real' names, it is surprisingly easy to identify someone via giving details of their life.