The number 15 route did indeed run between East Ham and Ladbroke Grove in the 1950's
See this website. http://www.londonbuses.co.uk/menus/rl001-100.html
'Dying a'int much of a living, boy' Outlaw Josey Wales

True drju, a lot of buses do seem to go east-west and vice-versa more than north-south perhaps, because of the river/congestion in central London - though 'Reelstreets' (the British movie-locations guide) says the location of this scene in question was the Hythe Road industrial estate, west London. ;o)

It is worth pointing out, I think, that when Buses came under the aegis of London Transport, many of the routes were a lot longer, often linking one side of London to another. For example; I live in Chiswick (west London), my mother lives in Streatham (south London). Back in the 70s, I could have got an 88 from Shepherd's Bush to Mitcham and, after a short walk at either end, done the journey on one Bus route. Nowadays, because of privatisation and different operators running shorter routes, I have to get 4 buses.
I think it's likely there were routes linking east to west London in those days, and people wouldn't have questioned it when the film came out in the early 70s.

I think this was probably just a prop period vehicle they had managed to get hold of - very few people outside London would be aware of the city's geography, or question what a bus bound for the East End was doing in Notting Hill!
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