Tiggy I am in London too and I think you underestimate that emotion played a big part in the remain vote here too, and I am also a northerner and spent a lot of time there before the vote, as well as spending April overseas, so I can contrast what I heard and experienced.
Speaking to remain voters here since, they were, as I was, shocked at how upset they felt the morning of the vote, physically upset or very angry in the case of the Under 25s. Discussing it I think it was an issue of identity. Many of us have at least travelled overseas, if not worked or lived there, and of course we live in a city where living with other cultures is not generally a problem, in general there is plenty to go round. Obviously there is deprivation and friction, we have had riots but I don't know anyone who thinks London is full. We felt European, and part of a wider world and overnight we were not. Logically I voted out of a understanding the whole world is now functioning within geopolitical blocks but also about feeling part of one, for all it's imperfections.
In the north the feeling was entirely different. Towns and cities where the industries that attracted high levels of immigration are largely gone, and I was hearing the we are full argument again and again, and a harking back to the 70s when it is perceived life was better. I was encountering a voiced resentment of both immigrants and London I had not heard before, even in rural areas where immigration is not actually an issue. Where it is they are not in any case in the main EU immigrants but the vicious comments about Polish people came out of nowhere. Except it wasn't nowhere it was clearly the Sun and Daily Hate. "you can't get doctors appointments" "have you not been able to get a doctors appointment" "well no, but there are towns where you can't" "Which towns?" "in Lincolnshire" "But the Eastern Europeans there are there to do the jobs there are not enough local people to do" "Well they used to come for the season but now they stay" "But if they pay taxes surely it is for the government to make sure there are enough resources " "But we can't afford it" . And time and time again, "it is alright for you there in London" . I might add I was also visiting old aged Britain, They voted to get back to a 70s I don't recognise......
Overseas from Asia to Australia everyone was bewildered as to why we were having a vote in the first place, the EU is perceived as a good thing doing a good job of representing Europe as a force for good. Since every country I visited was part of some sort of regional alliance they could not see why you would not be joined with your neighbours to exert more influence economically and politically. Time and time again I heard it put down to a colonial sense of entitlement.