Never been to LHR. Is it really worse than Turkey? In IST you can easily need to walk 25 minutes. They put the TLV flight at the farthest gate. Literally the last gate.
PE much worse, i flew from BUD-LHR-JFK on BA in F, had a 4.5h layover, we landed early and finally got to the 1st class lounge 20min before departure (we had massages reserved but never made it there) worst airport experience ever and thats with flying 1st.
The most i had to walk was about 20min in IST which i think is not that bad (and if your running late they will escort you through security and get you to the gate)