I have noticed that it is often the case that long-haul flights can be much cheaper if the starting point is somewhere in the EU other than London. I see people talking about cheap ex-EU flights all the time.

My question is just how do you find these cheap flights?

I am familiar with Itamatrix and use it myself to find cheaper days/times to fly but if I were to just randomly search for cheaper options for my next long-haul trip I would spend days or weeks searching with all the options available. So just how do you find those cheap ex-EU flights?

For example... I am planning a trip from London to Singapore for next spring. Clearly I could just fly LHR - SIN but if there were cheaper options that allowed me to fly to another EU city (perhaps with my avios?) and then fly from there to SIN then I would be very interested but I really don't know where to start... it seems like hunting a needle in a haystack!