Yesterday, I was inconvenienced by the fact that I couldn't get into the lower gears (needing to go up hills). So today, bike maintenance.
The problem seemed to be with the gear changer, and also with the cable adjustment. The gear changer wouldn't go into gears 5,6 or 7 (the higher gears). I opened it up, and the cable inside has become a bit frayed, and was fouling. So I got my side cutters, and gave it a bit of a trim, so that after that it could reach all seven gears. Then I readjusted the cable, so that I'd be able to change gear all the way from 1 to 7.
But I'm not sure how long this is going to last, so I went on to Ebay and bought a replacement gear shifter/brake lever, £9.99. Bike bits really are cheap!
Then I oiled the chain (when I see a rusty chain on someone else's bike, I have a strong urge to sneak over and oil it - the Phantom Oiler strikes again!). I checked everyting else, and it seemed fine.