Following the change they were rostered as deadheading out of their new assigned base (likely the one closest to where they're living) for flying duties in another base.
So if they lived in Bishops Horrible their assigned base would be STN (England & Wales), if they lived in Leiden then AMS (Netherlands), Paris then whatever ****e airfield RYR call Paris (France) etc., even if all of these were positioning to/from Germany to work from there their tax/SS would fall payable in England & Wales, Netherlands, France etc. ... Wouldn't it?