DMERTENS
From what I understand from someone who's already gone through the previous intake, the first day is a group assessment, team problem-solving. You will be told if you are successful or not at the end of the session. Don't be over assertive but also don't sit back and be a wall flower. They usually weed out three or four candidates at this stage.
The second assessment, I think, is an interview with Iago/TCX HR and a captain (flight ops). Usually down to about eight candidates by this stage. when finished they will ask the unsuccessful candidates to leave.
The third and final stage will be a full motion sim assessment. They will throw in all sorts of emergency situations, eg. EFATO, a passenger with a panic attack, etc., by the sim assessment stage they will probably have a good idea who they want. They won't tell you there and then but will send an email with the good or bad news
If you get through they won't start your training, probably until the Autumn of this year (TR) and base and line training until early next year as [a] there is a shortage of training captains [b] TCX are slap bang in the middle of their busiest season.
Best wishes and hope you make it!