i guess the journey back will be dictated by your journey to calais. if you have return tickets on the ferry or the eurotunnel you’ll need to get back to calais, probably by train although you can also take a bus.
to get back from bruges to calais by train is slightly tortuous. it seems to take about 3 hours, changing at lille or a 2-change strategy at kortrijk and lille. the best site i’ve found so far for booking tickets is this one.
if you don’t need to get back to calais then eurostar will take you back to london. eurostar tickets for may aren’t available yet. a single ticket is likely to cost around £40 from brussels to london. taking the bike will cost £30 if you can reserve a place on the same train as you, or £25 using the registered baggage service. detailed information is provided here.
my usual plea – any other ideas/comments/experiences very welcome!