Its a little obvious, but how well do you know him and how happy do you think he is in this job? There isn't enough detail here, but usually one person not per

Its a little obvious, but how well do you know him and how happy do you think he is in this job? There isn't enough detail here, but usually one person not performing could be a lot to do with his manager. Standard UK procedure is to engage HR and get their advice, which would be you documenting everything and lengthy PIP.