I am pretty sure that it is an Olympic A343 heading to USA or Canada. If you check out the tail and the left winglet you see the blue livery. Also the grey belly matches with Olympic. The contrail on the top belongs to an Evergreen Jumbo on the same airway a few minutes earlier.
UL0506 inflight from LHR to CMB. Amazing how much details are visible in this shot. Check out the red winglets, the registration on the right wing (of course not readable) and the dirt trace behind the main landing gear area!