I applied online a few months back. The process took approximately a fortnight. I interviewed at FDM Group.
Stage 1: Video Interview
Very easy. Webapp displays question and gives 45 seconds to think of your answer (or read prepared answers to refresh your memory) and then it starts recording for one minute.
Stage 2: Assessment day at one of the training centres (9:00am-3:30pm)
The day began with an hour introduction to company. During this first hour, instructed to ask person next to you a series of question to learn about them. Then after 5 minutes, you had to introduce the person to the rest of the group. Afterwards, we had a 30 minute maths test.
I recommend you revise GCSE level maths (eg Long Multiplication / Division, simultaneous equations, operations on fractions, operations on powers, Pythagoras theorem).
Next, we had three 5 minute interviews with different people.
After this, was 1 hr lunch break. No lunch is provided, but if you're unfamiliar with the local area, it gave you the opportunity to browse and look at the range of options nearby (btw 3 Pret A Mangers within a 10 minute walk).
IT aptitude was the next test. For me it wasn't great due to my lack of technical knowledge, but it was a mix of questions such as what does SQL mean but some coding logic questions with if else statements which require some thought.
Short tour of the building to stretch legs in between tests. Last test of the day was Set notation and Venn diagram test. You are given a booklet explaining how to do the Venn diagrams, but much better to revise and become competent before the event. The only question that required much thought was working out the Cardinality of the set as it needed you to use an equation given in the booklet.
I left there at around 15:00 or 15:30. Salary for both years is £18,000 basic. For the 1st year you get £2p/hr bonus which comes to ~£21,000 pa and then in the 2nd year, you get £4.00/hr bonus, coming to ~£24,000 pa. You do not get paid for the 9 week initial training period, but get a £20 daily travel expenses.