Try book.flybmi.com. I am having the same problem with their website but at least you can buy tix and get fares. We are flying SFO-LHR-SFO in March and are looking to fly LHR-BRU-LHR for a few days in Brugge, then a week in London. BD's fares out of Heathrow aren't that much more than Ryanair's fares from Stansted to Charleroi or Ostend, and hauling luggage between London airports doesn't sound fun.