we've just sent a letter to the Glasgow and Wolverhampton office explaining that he did not know the claim was being assessed on NI grounds and that he would like to make a new claim to be backdated , on income grounds and asking them how to proceed - in the hope they will send out a new form.
Thank you Gordon - the link you sent was to a new PIP form cliam.
I doubt very much that a letter will be of any help. if he did indeed make a claim for Contribution Based ESA then the information collected will be insufficient for him to make a claim for Income Related ESA. He needs to make a new claim from scratch.