Off work sick. Thought I'd have a go on @Minecraft PS4 to pass some time. Turns out they've updated everything, says my account is linked to another account - dunno how, not played for ages - and now I've wasted about 45 mins trying to sort it out to no use. Thanks @MojangSupport
We apologize for the inconvenience, but this is currently a known issue. The team is currently working on a fix that we hope to have out to everyone as soon as possible. Thank you for your patience while we work on the solution! ^RL