Whilst there I asked about the warranty (because my proof of purchase is for a 150 piece set) and they said the policy has now changed and if it says Halfords on it then they just exchange it. A handy thing to know I thought.
Receipt not needed, but they are now supposed to send it off and get replacement, so could be frustrating 
We have a spares case that contains 90% of the tool sets that ISN'T on the shelf. The correct procedure is to scan the the replacement part and then coupon 100% off the value, this generates the replacement item to come into store for the next person.
The only time we will need to send for the part is when it is a really obscure part of the set or its a old obsolete part not carried any longer.
All items/parts are now covered under warranty to try and prevent confusion in store over what was covered. In theory if you walk in with a stripped rachet you should have it repaired with a new mech, chances are you will get a new one.
Like everything in life the nicer you are to us the more likely you are to get someone who will go above and beyond to get you want you need.