London wasn't that great when it comes to tech jobs compared to US/Canada. Starting salary for grads at FANGs is around a third of what it is at large US cities when living costs are no more than 30-40% lower for example. Compared to rest of Europe London is a lot better with notable exception of Switzerland which is a non-EU country. So to me it would seem that membership in EU is not a necessary condition for good tech jobs with competitive pay.
I'd be a lot more worried about the general shift to working from home than leaving EU when it comes to London's importance as a tech center.
I'd be a lot more worried about the general shift to working from home than leaving EU when it comes to London's importance as a tech center.