The Thomson training course lasts about 5 weeks- and if EMA is not your base while you are there you will recieve extra money in your pay packet- I think around £20 per night that you end up staying.
Unless it has changed the first 3 days are about admin, uniform etc. You then get 2 weeks of customer service, followed by security, IMC, generic and aircraft specific exams. It is a really tough training schedule, especially if you have to do the 737, 757 and 767 exams (which I did).
Once you are on the line though the company are really good to work for. Most of the people are friendly, the hours are great as you can only do 4 flights between paired days off and there is the chance to do trips after 3 months.
I have no frame of reference as I have never worked for Monarch but I know that I do enjoy going to work