Eurostar will happily sell you tickets from Bruges or Amsterdam to London. However, in both cases, you'll be taking someone else's train as far as Brussels, then a Eurostar onwards. You're looking at a ~4 hour journey from both

(Eurostar were set to launch a service to Amsterdam, but then the Germans were very late delivering the new trains, which won't enter service until December at the earliest. Eurostar are still talking about doing it, but without a lot of details yet, especially not about how they'd handle immigration and security checks at busy stations, and how they'd handle Schengen-"domestic" passengers)

Given the airport options available (or not) near Bruges, I'd probably still look at Belgian domestic train + onwards Eurostar from Brussels, on a through ticket booked with Eurostar. I'd probably fly back to Amsterdam in your situation.

Another option, only slightly slower - morning train from Bruges to Lille, nice lunch in Lille with a short wander round (there's left luggage at Lille Europe station), then shorter Eurostar trip from Lille to London.