the effects of Brexit on travel for dance
The first rule of being in the UK: Don't mention Brexit!
The 2nd is not to mix up English, Welsh, Scottish and N. Irish (or N. Irish with Eire). The former are all part of a [Dis]United Kingdom.
There are other things not to mention for a peaceful evening! (e.g. avoid flags).
Impact on travel - it used to be more that you joined those from other 3rd countries to queue for entry (and exit - you need that exit stamp!). Now, as nearly everyone in the world moves to e-gates and e-visas (ah, the immigration and refugee issues) perhaps it's becoming less of an impact - but we'll have to pay.
There should be an impact on non-nationals coming to the UK to teach. Many Argentinians, however, qualify for Spanish passports - which is in the EU, with 'exceptions' (maybe). I'd guess some work in the 'black economy' on a tourist visa. Taking live music to the EU has become prohibitively expensive - and I guess it's reciprocal. I understand some 'world music' events in the UK got cancelled because of immigration restrictions on performers.
There's also a massive difference between cultural support in the EU and UK (Some EU countries provide support).
The secondary impact is air travel prices. It still costs more to take a train to the EU than to fly. There's also a cost-of-living issue with prices - different than the 90's!
I suppose the major impact is personal. I used to feel 'European', but that got taken away. Whilst my heritage is mainly 'English', it's not really something with which I identify - or wish to promote.
Whilst many in the EU speak English (computer tech, education, etc), fewer UK citizens know any foreign language, and dialects of English can be difficult to understand. Many decades ago I had an interest in a girl from Glasgow. We decided our best common language was German. It helps, for acceptance, to have another language besides English - and to appreciate the culture.
if I do travel in the near future, it's likely to be to London
There's a website of London Milongas. Outside London, depending where you are, there are other sites which try to co-ordinate locally. No one could agree on a unified platform for the UK. Don't trust FB without checking!
If you can, get out of London. Anywhere! The further north or west the better. It can be very pleasant. AT may be popular, or sparse, or in a dead zone. Scotland (in places) is quite good. But don't expect easy travel. Trains may be cancelled, roads may be flooded or full of potholes, or congested, or collapsed - but it may be quicker than air travel within the UK.