hi there i am dean i currently work at peugeot and kia as diagnostic/master tech. i would be happy to assist you with your problems
With your depollution fault you have with your car a cat cleaner and fuel filter will not help the fault, The Light is basically your engine management light has came on, Your engine ecu will have a fault code stored in it. The best thing to do is have the fault code checked with a garage with the correct diagnostic equipment. Which will give you a fault code. Once you have this you will have a better indication where to look for the fault as it will tell you a certain part of the system.
Im sure kwikfit are reading fault codes, I would do this first which will save you money in the long run instead of throwing money at cleaned etc,
hope this helps, once you have a fault code and description come back to this question and tell me the fault code and i can assist you further,
The code should look like p0301 something like that.
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Number 20 in the diagram is the fuel filter
It is underneath the car just in front of the fuel tank held in with one bolt, and 2 push clips for the 2 fuel pipes.
should take you 5 mins to change.
Hope this helps