Got a technical interview a few months after my telephone interview. Shortly got an assessment center after that. They have sites all over the UK where they hold interviews, alert them to what is most convenient for you. They changed mine from Aberdeen to Sunbury as it was closer for me.

Multiple online interviews consisting of pre-recorded questions, to which you record your own answers to. You have 2/3 attempts per question. The second interview consists of problem solving questions which increase in difficulty as you go on.