Long Time lurker but have finally joined FT to follow threads like this as I'm always interested in cheap premium flights from SEA (Sin preferably) to U.K. (Man ideally).

Echo the other guys comments about following the usual sites (& would sign-up to the carrier's FF schemes & promo emails), 1 site that occasionally has some awesome deals is secretflying.com, register for the UK & Mainland Europe daily deals newsletter,

Also 2nd pulling the trigger when you find a good deal, recently missed out on Sin-Man-Sin Business class with Finnair at s$3,200 because of a mate dithering about dates, it's now s$4,600+