if you can start from GLA or EDI, why the need to fly one of the 'long' CE routes? Surely GLA/EDI - LHR - XXX will do it - maybe Amsterdam for frequency of flights and easy back to back? I can see sensible routings through LHR for under £500 (and slightly cheaper through LCY but with stupid 30 minute connections...)

you might get cheaper, but if you start in GLA or EDI, you don't really need to look for a 'long' route do you?