Commenting on my own blog, Ben said: I think (I'm pretty sure, but if you still have the specimen or better photos?) that your boring grey moth is in fact the very rare Sombre Brocade.
It's very similar to a plain Brindled Green, but I think I can make out the markings from your photo. This prompted me to go a-Googling as I had never heard of the Sombre Brocade, and indeed it is not mentioned at all in the first edition of Townsend, Waring and Lewington because it only made landfall in the Channel Islands in 2006 and in Dorset two years later. But it appears to be spreading and so I felt it was worth posting closer-up pics of my moth (now gone, I am afraid), just to see what the many experts here think.
I have borrowed the 'standard' pics from a post in September from the Portland Bird Observatory which I think everyone will find interesting in any event. As I said, I realise that the condition of the moth and the quality of my photos make this a rather academic exercise, but I'd be grateful for views. I still incline to Brindled Green. Martin Wainwright, Thrupp, Oxon