Hello my name is ***** ***** I will help you with this.
If you are the tenant then no.
The Council can not charge you for letting it for so many people.
If the Landlord did not know then the wont charge the Landlord either
Also you wont have to pay extra council tax for the 5+ people
But the Landlord may ask you to ask the extra people to leave
Can I clarify anything for you about this today please?