Informal at best. Basically just a chat about yourself past work experience just to get an idea about you as a person. Pretty much like meeting someone at a party and introducing yourself. There is a work sample where they set you a simple task. You need to listen to instructions and just do it. Even a zombie would pass this.

The interview was surprisingly easier with almost no barrier to entry. A lot of the workers there are not native to the UK, and I guess because of the nature of the job it's only required that you have very basic maths and english skills. The interview is basically just one test for each maths & english, and it's something you could likely do in primary school (though surprisingly a few people in the group actually did fail). The interview isn't individual, you'll do it with groups of 10 - 15 probably. Out of those 15, maybe 3-4 will fail somehow, but as long as you know basic multiplication, and subtraction, you should be fine.