Thanks for the links and information, gentlemen.
I'm an admirer of Bob Jackson's work and attitude, but, eyeballing that removable section in Bob's link, I wouldn't be overly happy riding on it. It seems a bit too race-weight to me. The S&S section in Dan's link eyeballs more solidly, and S&S have built up a lot of trust over the years.
Hey-ho, I know a Raleigh like that DL a couple of houses away, which came to the lady of the house from her late father, and which she occasionally rides with me. The particular bike in George's link was advertised and sold by a fellow I've known for years on the net, Andrew Muzi of Yellow Jersey in Madison, Wisconsin, a town evidently from the photograph so dull that at 6pm every night they roll up the pavements, which doesn't stop Andy Muzi from being a dry wit and an expert on the better bikes from whenever.
I agree with Martin: the Chainglider is a sensible, solid alternative to the Gates. It is also superior in some ways. For instance, a Gates belt ridden in the wet or mud will transfer filth from both wheels to street trouser ridden without bicycle clips, and let the trousers be caught in the cogs too; I ride a Chainglider in street clothes and don't even own trousers clips because the Chainglider doesn't let my trousers bottoms get either dirty or caught in the cogs.