Was it one of these? There's a few hoops to go through and fees to be paid.
https://uk.usembassy.gov/visas/temporary-employment/overview-2/
I've worked and travelled extensively usually with my employer dealing with visas and work permits. Lets hope in future following (if it does happen, can but hope it doesn't) brexit UK/EU travel and in particular work visa/permits are considerably easier than USA or many of the countries I've had the pleasure of working in.
How about the students and young working travellers? Found this for Erasmus students
https://www.bbc.com/news/education-47293927 haven't time to read in depth but there seems to be more questions than answers.