@jackdaw
Your search engine results may vary but top hit, for me, was estimating about 8.5-8.6m Londoners, which might split 75/25 for Remain.
2.8 million immigrants (the page said) but who knows what their various attitudes to the EU may be?
I've seen, in a book, a map of the UK where parliamentary constituencies are drawn with equal areas (intended to reflect the disparity between land area and number of voters, supposedly the same in each) and London is a huge blob, taking up most of the shape, with the shires as mere appendages.
If I ever find it (or an equivalent) online I'll post a link to it. Otherwise, try local library for an atlas of the British Isles, published late 60s/early 70s, broadsheet sized and about an inch thick.