It's something I'd wanted to do for a while, especially once I'd realised how large my London cluster was getting. I mean, it wasn't actually all that big compared to my main cluster, but it was a lot larger than any of my other isolated clusters, plus it was pretty compact, in that there weren't many missing tiles in the middle of it.
While my route into London was a little circuitous, that was mainly because I'd specifically picked a way that kept me on suburban roads and away from the main roads for as long as possible, so it turns out that I was crossing off most of the tiles I needed without having to go too far out of my way. In fact there was only one point where I had to go down a route then pull a u-turn and come back the same way to get a tile, and that was before I even got into London itself. Admittedly there was the Swains Lane (nearly) loop which added two extra tiles, but I was wanting to do that climb anyway, so I'd have got them eventually even if I hadn't done them today (and it made sense as I was going right past it).