The enforcement period for outright planning permission is 4 years and for lack of building regulations 1 year. For change of use it is 10 years. Hence, this is out of time for enforcement by the local authority. What would normally happen is that he would be asked to provide an indemnity policy when he sells the property because that is the quickest cheapest and easiest way of dealing with it.
Alternatively, he can apply for a certificate of lawful use or retrospective planning permission. He may not get retrospective planning permission and the certificate of lawful use process is extremely convoluted.
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