You are not permitted to sublet part only of your property (i.e. letting out rooms / taking in lodgers etc.).
You are not permitted to sublet the whole of your property, unless this is via an Assured Shorthold Tenancy agreement. The tenancy agreement entered into in this regard is required to contain a covenant on the part of the sub-tenant to abide by the terms of the Lease (save for the payment of the Service Charge).
For the avoidance of doubt, short-term subletting of your property on websites such as Airbnb are therefore strictly prohibited and if your property is sublet in this manner, this could result in enforcement action being taken against you.