The "2nd Politics of Bisexuality Conference" was also in London, at the London Lesbian & Gay Centre, in April 1985.
Booked into London's new Lesbian and Gay Community Centre, the 'lesbian sex wars' of the time meant that bisexual groups were banned from the Centre. (Their mere presence would oppress lesbians, apparently.) Other groups banned included anything to do with BDSM. One 1990s book on the sex wars has a lot on that, but the bisexual ban goes virtually unmentioned.
As the booking was accepted "in error", it was allowed to happen at the Centre and the ban was eventually overturned in June 1985. (To give an idea of what things were like, someone took along a picnic including some champagne to the meeting on the bans. When they opened the bottle, there were people who seriously thought they'd heard a gunshot. The Centre eventually closed in 1991, just before the London Bisexual Group were going to hold a party there, after the safe was robbed without any sign of force being used and the insurers declined to pay out.)
On the weekend itself, the proposed programme was thrown out at the start and a somewhat disorganised event followed. One positive result was the decision to do a book on people's experiences of being bisexual. This led to Bisexual Lives, one of the first books on bisexuality and the first by and about the community, being published in 1988.
