Derailleur Damage

Bit of angle iron cut to a little over half the radius of a 700c wheel. Drill two holes in it - bolt one side to the derailleur hanger, put a bolt in the other side and screw in/out to act as the 'feeler'. Works fine, if a little clunky. If you bend a lot of hangers, then I'd suggest buying the proper tool.

I didn't say that all workshops would charge £20 and require booking - independents wouldn't, but take it to a big retailer and they probably would. All I said is that it's possible to do it yourself with basic tools (hacksaw/drill/nuts and bolts). I know DIY isn't for everyone, but it's not absolutely necessary to take it to a shop.

Fair enough, I'd still say take it to a bike shop because it'll be a better job but then, I did just tweak the hanger on my pomp into shape at home the other day with an adjustable spanner because I couldn't be bothered riding up to the shop!