The bendy-buses are still out there causing havoc so don't think that's the only reason for the single-doored P4s.

I <3 the P4 - especially during school holidays. During term time, I go to Denmark Hill and catch the train to Victoria since it just takes too long to get through Dulwich Village between 7.45 and 8.30.

Double-deckers would be good though - it does get ridiculously busy at times. To be fair though, the 176 and 185s are just as crowded. There are many mornings when you can't get on the P4 beyond the Horniman and the 176/185 is standing room only by the Plough.