It's much harder than it used to be. EU citizens now need a visa to stay and work for longer than a few months, and they mostly need to obtain a Skilled Worker Visa which has occupation and salary requirements.

Since Brexit I've noticed that my London-based employer has had an uptick in hiring Indian and Pakistani nationals, especially in Dev and QA. It's probably not the outcome that most Brexit supporters were gunning for, although I did hear that a large proportion of South Asians did in fact vote to leave for this reason.

if you're from outside, it's more or less the same. if you're from europe, it's harder (but not that much harder if you're in tech).