Brilliant replies...
Tyres - yes, I guess they may not be very grippy, not to mention cracks etc... I'll keep an eye on them. The bike has just had a new MOT, so it should be basically OK. I'll get some engine oil from the first available garage in case of leaks or high oil consumption, and I'm taking a torch and a tool roll... Yes, WD40 is a good idea, especially as it seems to be still snowing in Scotland... Not a thirsty bike, but not a large tank either - I have no idea of the maximum range, but I'll find that out one way or another.
As for the route, my main worry is breaking down on a motorway. I have breakdown cover, but it would be a real pain, and I wouldn't have any choice but to ring the green flag man. Yes, the battery might well be a problem. Daylight riding only, I thought.
Very generous of you to offer hospitality, John R! Thanks, but I hope I won't have to trouble you!
Yes, agree about it being a little bike with few moving parts, which is just what I want. The rider may also be a non-moving part by the end of it. Bullet-proof - good to hear that... Greatly cheering to read your responses - thanks to all!
Martin
PS And it can't be as bad as the clapped-out Bantam I had when I was 17.