I've finally found a solution (thanks to Google, of course), so I thought I would share it with any of you who aren't already in the know.
You only need two basic kitchen ingredients - bicarbonate of soda and cooking oil.
Mix equal quantities of them together (I used a tablespoon of each today and it was plenty for the two bottles that I wanted to clean). Then spread it all over the glue and wait for thirty minutes before rubbing it off with a pan scrubber. My scrubber is just a cheap nylon one, but it did the trick. After that, give the jar a good wash in warm water and washing-up liquid to get the oil residue off it.
The first time I tried this, a couple of days ago, I was a bit hasty and only waited ten minutes. Even so, most of the glue came off, but I did need to put a bit more paste on one or two patches and wait a bit longer. However, next time I'll try to be a bit more patient, though it's not my strong point.
I hope it works as well for you as it has done for me
![Very Happy :D](./images/smilies/icon_biggrin.gif)