Today, I replicated Nathaniel's walk to Hendon and ended with a pint in the Greyhound. And very welcome it was. I chickened out of walking back, however.
The route was rather different from Nathaniel's as I avoided main roads as far as possible and took in Regents Park, Primrose Hill, Hampstead Heath and one or two other parks. If any one wants the route, send a message and I will detail it. It took just a shade under three hours from Richmond Buildings to Hendon.