Ignoring the outliers, the competition was between BAe/Pilatus to licence build the PC9 at Warton, the Shorts/Embraer to build the Tucano in Belfast.
The UK government at the time had a tiny majority and were being propped up by the Ulster Unionists. So, despite the PC9 being the better aircraft, the contract went to Shorts - but then the RAF made things worse by demanding various major changes from a pretty capable Brazilian aeroplane - the most significant being the engine change, but also they tried to cut costs by putting a lower standard ejection seat in it.
And so the RAF was landed with a training aeroplane that needed 150lb rudder pressure and 100lb stick force to recover it from the spin, with occasional differences in handling qualities between airframes, only limited interchangeability of parts, a disfunctional ejection system which wouldn't allow ejection on the ground or canopy jettison in the air, a gear selection mechanism which didn't readily allow the instructor to override his student, a pitch trimmer which regularly ran away, and running costs around four times what were contracted.
Much of this might have been sorted out if the aircraft had been handed over early to Boscombe Down and they were resourced to analyse it quickly and force rectification. This didn't happen because the aircraft came on line just before the Gulf War, and for entirely good reasons all available resources were diverted to war-tasks. Much of the reporting of the Tucano flight trials only happened 4 years after they were actually flown - by which time the RAF training system had just bedded in to make the best of a poor aeroplane.
Personally, I'd recommend that anybody wanting a civilian aeroplane in this class bought a PC7, not a Tucano. Or at-least, not an ex-RAF Tucano.
G