Hi Michael
He can either put in for a change of circumstances - which will trigger a review, or he can ask for his review to be brought forward. People use a change of circumstances to inform the DWP that their condition has deteriorated. This may be appropriate, especially as he lost his daily living and didn't know the system or perhaps wasn't well enough to challenge it. If, after an assessment, the DWP agree and a claimant is given an improved award, the money is back-dated to the date that the DWP was informed of the change of circumstances (however long it takes).
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
