I Applied in December 2017 and did not hear about being invited to an Assessment centre until March 2018, so I had forgotten I applied. I was not going to go, with the cost coming to around £150 for travel and hotel, which was not reimbursed. I always find this a bad sign. Speaking to my HR contact, he was very convincing that the assessment centre would be worth the cost, and in truth it was.
Started out just chatting with other candidates and then current graduates joined to chat to, asked them plenty of questions and help build on the research of the company previously done. There were two individual exams, brush up on basic SQL and algorithms, along with you aptitude skills for these. The one on one interview went well, showing knowledge of the company is very good, and make sure you keep calm and be confident in what you are saying is answering the questions, this leads to a technical interview, you do not have to show code but this helps to explain your logic, remember to speak out loud what it is you are thinking, even if what you are thinking is your, it is good to show your working out, if you just say the answer after 5 minutes they may think its a lucky guess or if its wrong, showing your workings may show them you were on the correct path at least. I enjoy algorithms, I find them as fun puzzles, but do practice if you do not work with them regularly. (key is to think how you would do it manually and then think how a computer has to then think the same way). the group exercise is fun, a few red herrings thrown in to throw people off and test communication and logic, very basic maths required, make sure you are clear and constantly check the information unique to you.
Ask plenty of questions through the day, but do not ask dumb questions just to look engaged, listen to what is being said and ask questions based on what you have been told, show your interest.
The offer was very good, the location was Holborn which I said I would prefer and the finances are a lot better than what was advertised but a different opportunity spiked my interest and I had to sadly decline, but I got a very good feeling and will possible rue my chances missed... Also one current graduate hit on one of the candidates and asked for her number! Ballsy!