Not sure I can agree with your logic Betty Girl as limiting it to just people who work on UK registered aircraft seems a very artificial boundary. Where do you realisticaly draw the line?
What about non UK nationals working on other UK registered "bases" - be it shipping or haulage?
Or local employees on UK military bases (ie British soil)? Gurkhas? Different rules apply to those based in HK before 1997 and after ... on the basis that they were
based in HK prior to 1997 -
Court of Appeal emphasises where they are based and where they are expected to retire to is the important criteria.
Or turn the logic around - could a UK based airline register their aircraft elsewhere and retrospectively apply local terms and conditions to UK based employees who work on the aircraft?