It really is difficult to know what levels the aircraft were at. I have taken pics through a telescope of aircraft at 30000 ft which look like yours. Equally I have taken pics of similar aircraft at 6000 ft with a 50mm lens which also look like yours.
If they were not overflying they could possibly be Luton inbounds under radar control of the TMA controllers at West Drayton. If they were 8000 or below they might have been inbound to Heathrow from Ockham and being routed over the ILS for a right-hand circuit.
Separation in both cases would be a minimum of 3nm OR 1000 ft vertically.