Looks like a clear case of ATC getting into the pilots' business... It is NOT his job to question whether you are "minding the steps"! Since he cannot see the entire cockpit setup, he is totally UNQUALIFIED to make such a judgement!
WHERE in UK ATC regulations does it allow for a controller to "reprimand" a PIC for an MCP setting? While I might understand a controller QUESTIONING a setting IF a breach of clearance is imminent, a controller does NOT fly my airplane!