A tenant being jailed does not automatically give rise to the tenancy being discharged. If you want possession of the premises back, then you will need a court order. There are a few methods of doing this. Firstly, you can use a section 21 notice if you have a fixed term tenancy which is due to end soon. Secondly, you can apply for a section 8 possession order based on rent arrears if applicable. Thirdly, depending on the crime, you can apply for a section 8 possession order for serious antisocial behaviour or illegal use of the property.
If the tenant’s belongings have been moved out of the premises, however, you can rely on the doctrine of “implied surrender” to retake possession without needing a court order.