I always try and start my long-haul flights outside the UK now. Two recent examples with one-way flights from Turkish Airlines and Lufthansa:
LHR-IST-HKG (2 hour connection) = £460
LHR-IST (48h stopover) then IST-HKG = £350
So the £110 saved paid for 2 nights accommodation and all spending money in Istanbul.
LHR-FRA-SFO in F as a mileage redemption, taxes = £450
Just FRA-SFO without feeder flight, taxes = £250
So the £200 saved paid for a flight LHR-FRA (£69 with BA) and a night's accommodation in FRA.
It's ridiculous how the money saved can give you an extra few days holiday in a different country.