Non-resident self-employment

Dear All,

I am a UK citizen (London born and bred). However, I have not lived in the UK since 2005.

At the moment, I am a resident alien in America (so I am not resident in America, legally), where I work full-time as a university professor on a J-1 visa. The J-1 visa restricts the work I can do to my job at the university. I live and work in the USA pretty much full-time.

However, I would also like to do freelance work (as a researcher) with clients who are not based in the USA (they are based in Switzerland). The work would also occur outside the USA (in East Africa).

The clients who contacted me require, under EU regulations, that I register as self-employed so that I can do the freelance work and pay appropriate tax.

Can I register as self-employed in the UK for tax purposes?

Could I use a friend's address as the business address?

If not, is there any other way I could do this work?

Any advice appreciated.

Best,

James.