1. As I understand it getting a work permit on the basis of being a British citizen wanting to be an airline pilot in the US, pre-Covid was difficult enough...it certainly wasn't something that many people managed to achieve. KARNAK66 has explained why getting a work permit now or in the foreseeable future is going to be mighty mighty tough.. eckhard's solution isn't that far fetched...
2. Even getting experience in mainland Europe (specifically one of the EU states) now we are post Brexit could be difficult unless you have the right to live and work in the EU.
3. In the short term you might want to look at UK/CAA/EASA options in the short term whilst the fallout from Covid manifests itself and we get some idea how/when recruitment anywhere is going to pick up.