Such a subliminal message might be "constructive dismissal" and against disability legislation. With a good lawyer you might get a decent result if they ever did fire you? On the plus side, the fact they haven't fired you means either (a) they do actually value you performance even if they're claiming otherwise (perhaps to avoid paying more) or (b) they'd quite like to fire you but fear being sued big time if they did, so holding back. Either way, it'd seem you've got some power over them if you play your cards right. So, maybe try not to stress? ;) Yeah OK that's easier said than done....