It’s all supply and demand. Right now the supply for U.K. airlines is far below the demand. Especially experienced folk.
Once this demand reaches critical they’ll go running to the CAA and will be forced to issue work visas which keeps operations going. Supply and demand balances again!
The issue is that EASA will NEVER reciprocate that deal for U.K. passport holders so in the long run the U.K. pilots will be disadvantaged.
This “shortage” of U.K. Pilots is a very short term problem I suspect.