Stop delivering these letters to me

For a while now I have been getting these letters that are addressed to someone else.
At first I just returned them straight away but I realised that the postcode is wrong and is actually the code for the opposite side of the street. So as the IR aren't getting it that this person DOESN'T LIVE HERE, I am now considering actually knocking on all the doors across the road to see if I can find the right person.
Ridiculous that they don't know their own address though...I also got a few letter for someone else with the same Postcode so someone is obviously really mixed up.