immediately write to the grant authority and state that you wish to be assessed for the top-up grant under the 'change of circumstances' provision, as you don't have an income and therefore have no means of support;
that should do the trick;
you will most likely have to produce a mountain of supporting documentation, eg current p45, p21 for last year, etc but as long as you produce the documentation you should be alright;
if your application fails, appeal the decision through the appropriate channels and continue to do so until they eventually grant you your entitlement;
best of luck with your studies.