Hello all,
It didn't seem runny enough to be oil, but maybe it was dried by the passing air on the ride, and/or the coldness of the air - dunno. Maybe it had been there a while and I'd not noticed. But anyway, general consensus seems to be oil rather than grease. Fair enough, I expect that's right. Went for a short run this morning - just two or three miles - and there was little if any on the brake plate when I got home, maybe a little bit, and some around the brake plate nut - hard to tell much very precisely because of raindrops all over the place (unexpected shower, but actually, living in South West Devon, not all that unexpected.) I'll look into it further as soon as I get time (moving house next week so a bit pushed for time at the moment), including taking the wheel off and having a look at the brake. Looking forward to that, and maybe also then taking the forks apart to learn about them. If and when I do that you can expect a flurry of dim questions.
Phil