My question is why? The only thing I can think off is that it is seen as a problem for a single deck bus to turn left out of Honor Oak Park into Stondon Park. But its no worse than the left hand turn the 2 decker 171 does out of Borckley Rise into Stanstead Rd.

Indeed I've noticed that sometimes the P4 does a !72 loop" around the Chandos rather than turn left into Stondon Park - which just delayed things.

Doesn't make a great deal of sense to me. But thank you for the heads up.