Slim, medway is right you can route via sivda and UP155 to either somva or redfa on the london/maas boundary that would take you way from london.
as for the FL270 35 B4 Lam restriction, its hard we are aware its restrictive and that you would like to stay higher but the idea is to get you below all the crusing traffic over london at FL300 plus, it would be an absolute bugger to get you down when you want. Routeing you further north is not really an option as you would crossing the tracks of and be descending into the teeth of all the departures from the TMA going east. And obviously we don't have the option leaving you high and descending later because of the military/uncontrolled airspace over East anglia, lincolnshire etc. The mil wouldn't want to know and we are too busy to provide you with a RIS/RAS and against the traffic out there. We are simply too busy with the stuff inside CAS to do that.
you should be able to route SW to BCN on weekends and in the evenings if you are happy with a service from the mil, EGBB departures do it so i can't think why EMA depts can't. I'm sure someone else will tell me if i'm wrong.
