On Long haul J with aisle access (so not BA CW!) it appears to me that reclining a seat doesn't affect the safety of other passengers.
As someone noted already the issue isn't just about access to evacuate ... it would be nigh on impossible to test the crash resilience of a seat in all possible positions and so the seat is tested (and approved) in one position and that is the one you need to be in for takeoff and landing.
Numerous other positions of the seat may also be safe, but it has only been proven to be safe in one position, rather than shown to be dangerous in all other positions.