Hi Alba
You are absolutely right! I understand why someone might be saying that, but it isn't a valid reason that he can use when applying for PIP and he should not be putting that on a form - it would almost guarantee that he would be rejected. He will want to say that his disabilities/conditions have deteriorated so that he can no longer work full time - but he should not talk about any perceived financial benefits!
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
