Very lucky they were
It would appear from reading the AAIB report that not only was the Captain not fit to fly but neither was the aeroplane with an elevator coated with slush.
Since the elevator trim gave reversal - does anyone who knows the Jetstream 41 - know if it is a tab that acts aerodynamically on the elevator - that would explain that methinks.
Sounds like they lucky missed (probably down to the extensive experience on type of the Captain) the third mistake that could have caused a tragedy. Too many holes in perfect aligment there lucklily the last one like their elevators hinges was blocked or the story would have be quite different i suspect.
For sure he was under pressure to GO but deep down he suspected he was pushing his luck - hand flying and not using the A/P to make sure things were OK I wonder being a contractor - if he would he not get paid if he had backed out of taking that flight at such short notice.