Just before the Brexit referendum I was wondering how Brexit would affect the kind of people coming to work with us. That's a long-term effect and very hard to measure. But really, like most of the country I hadn't really thought deeply about the direct practical consequences of an Exit vote, in this case the consequences for research that would show themselves within the first month.
The effect is on EU funding in particular. Since the UK hasn't actually left the EU, you might think that things carry on "as normal" until that point - existing projects continue, and you can even apply for new projects. (In fact, that's essentially the official guidance so far.) The problem is that collaborative EU grants are the lifeblood of a lot of research, and they're also very competitive. I know of at least one colleague who's been taken off a grant proposal (which is being organised by someone in another EU country), because a UK partner now means a risk factor that could easily cause a reviewer or a programme administrator to mark the proposal down.
Similarly, at least two colleagues who have been leading on EU grant proposals, they're now in a difficult situation. After having put a lot of work into preparing a proposal, do they submit and risk getting marked down as a risk factor? Do they rewrite the proposal with Brexit backup strategies? Do they stop and wait to see what happens?
(I'm not writing this down to change anyone's mind about Brexit, by the way. Just documenting.)
Less concrete, but in my own first-hand experience: we were intending to invite a good researcher to come and work with us under the Marie Sklodowska Curie scheme (which funds researchers to spend time in another country), but I'm not sure how we can do that now. The funding is still there, but apart from the "risk factor" effect mentioned above, the potential researchers would obviously need to know how it affects their right to work in the UK (will they need a visa?) and what career options might follow on afterwards; and there's pretty much nothing we can say in answer to such questions.
This Guardian article, "UK scientists dropped from EU projects because of post-Brexit funding fears" puts the same phenomena in a wider context. This quote, for example:
Joe Gorman, a senior scientist at Sintef, Norway's leading research institute, said he believed UK industry and universities would see "a fairly drastic and immediate reduction in the number of invitations to join consortiums. [...] I strongly suspect that UK politicians simply donât understand this, and think it is 'business as usual', at least until negotiations have been completed. They are wrong, the problems start right now."