Claiming Council TaxWatch
The university say they can only issue exemption certificates for one year after graduation, so how else does he prove he was a student?
Student life, in partnership with UEA
Then produce it at the magistrates court if the council sue him and demand his costs.
Councils have notoriously poor admin, a very aggressive strategy to detract from it and a huge paper backlog that often drags on for years.
They pursue full time students over erroneous council tax claims so often, then lose at court and have to pay the student's costs.
Your flatmate doesn't have to prove that he was a full time student and not liable to pay council tax.
The council has to prove that he was liable for council tax.
Misleading the court when they are aware that he was a full-time student is against the law and would be taken very seriously.