Peugeot TU Misfire - Fuel injector replacement

How to fix a misfiring Peugeot or Citroen with a TU engine. This particular one is a 2005 Peugeot 206 1.1 The car was making a noticeable misfire sound, and was down on power (which is bad in a 1.1 206 because it needs all the power it can get) Injector number 3 had failed and had to be replaced, it was an easy thing to fix for £30.