Thanks very much for the replies, quite helpful.
I just had a look around a local second-hand/bike recycling sort of place and considered some options. There was a relatively cheap (twice what I paid for my Dawes six years ago...) 24" road tourer (27 x 1 1/4 inch wheels) that could cheaply satisfy my immediate "need" for a UK tourer and winter commuter (it has mudguards) and leave my money mostly untouched for when I might want to get something rather better for a much longer tour. It had a much more compact frame than my Dawes or my current old racer, which felt comfortable actually - since I'm more legs than torso. I fear that pannier heel-strike could be an issue, though, so I've come home to get some other racks and my panniers and I will go and see what I think.
Oh, and would you believe it, as I was cycling just now a bright red bike caught my eye, locked up outside a house, and the blurred shape of the downtube logo made me stop and go back. Sure enough, it was a Thorn Sherpa! I might have to leave a note on it asking the owner if I can come and have a look at it.