There are several types of tenancy misuse and fraud. They include:
This is when a tenant says they're living in the property let to them but instead lets all or part of it to someone else without the landlord's consent.
The tenant vacates the property and hands the keys to someone else in return for money, a favour, or in return for money owed or goods received. Once the keys have changed hands, it's classed as unauthorised occupation.
This can happen when a tenant claims that the council property is their only or main home but instead uses it as a second property and lives there only rarely or not at all.
Wrongly claimed succession
This happens when, for example, the home occupier isn't the person who would be entitled to take on the tenancy after someone dies: They don't have the right kind of relationship with the former tenant, or they haven't lived there long enough.
Fraudulently obtaining social housing
This can happen when the tenant gives false information to obtain the tenancy.
More information on tenancy fraud can be found at GOV.UK
You can report suspected fraud here