I've been a bit quiet - I managed to push my square up to 39x39 (you can get over to Holwick Scar from Lunedale, just), and knocked off a load of tiles in the Lakes, and planned a grand procession home to knock off the linking tiles and make a coast-to-coast, but I shagged my knee, and since then I've been slowly recovering and ticking off a few more as circumstances permitted.
Yesterday, I finally rode Thistlewood Lane down into Wolsingham (Oakey country), and today I knocked off a few more around Alnwick and Shitbottle. I reckon I only need a dozen or so more tiles to link my cluster up into Scotland (currently 3466). The square is going to be a right bastard to extend, and I'm probably going to need to dig out some hiking boots as there are no tracks up in the Pennines.