Hi Evo,
WBS is correct. OCK - BUR is impossible. Far too close to the climbout when Heathrow is on Westerlies, and right in the way of the ILS traffic for 09L/09R on Easterlies. Take a look at a map. Plan to route OCK - West of Fairoaks LFA - Ascot Racecourse - BUR NDB (or town). Anticipate a clearance not above 1000ft ASC- BUR SVFR. Elevation of Ascot is 220ft. After BUR you may get climb to 2000ft. BUR - HEN is fine. A transponder would be useful and be sure you listen out carefully on 119.9. Be prepared to contact Northolt (WBS's mob) on 126.45 if so instructed. There is the possibility of a refusal, since we are required to provide standard separation in Class A airspace, and if somebody is already in the Western part of the Zone this is difficult to achieve. Talk to Heathrow Radar anyway and they will advise.