I didn’t notice him as the light-voiced gay magistrate in Shadows in Bronze (one of Mary Cutler’s Falco adaptations) until he was announced in the final credits. I’ll listen out for his voice the next time it comes round on R4E to see if it’s really a similar style.
I think he did use the same voice as Mr Preston, the sinister stalker in Wives and Daughters. That’s certainly a character out of the same stable as Rob.