According to The Worldwide Guide to Movie Locations (
http://www.movielocations.com/movies/o/oliver.html),
"The ‘London’ streets – yes, even the steam railway – were built on soundstages at Shepperton Studios, Shepperton in Middlesex. Despite what you may read, the crescent used for ‘Who Will Buy?’ can't be found in London, nor is it the Royal Crescent, Bath. It was built from scratch, from designs by by Production Designer John Box, on the Shepperton backlot."
Besides the Royal Crescent in Bath, Bloomsbury in London looks somewhat like the set location.
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Henry Miller