Hi Francis,
Because all new claimants for sickness benefits can no longer apply for IB, (from November 2009 IB became Employment Support Allowance aka ESA) there is a massive backlog which is most likely the reason why you haven't been come up for a 'normal review'.
However, don't be concerned, your IB cannot be stopped unless you have been medically examined and a DWP Decision Maker has written to you and told you that you no longer qualify for IB.
Hope this is of some assurance.
Best wishes.
Jim
PLEASE READ THE SPOTLIGHTS AREA OF THE FORUM REGULARLY, OTHERWISE YOU MAY MISS OUT ON IMPORTANT INFORMATION. Nothing on this board constitutes legal advice - always consult a professional about specific problems