At what point should we take possession?

Tenancy Types and Management

After serving a Section 8 we have a court hearing on 28th August, as tenant is 3 months in arrears. We have also served a section 21 giving notice to tenant to leave on 21st Sept.

Today, our Agents advise that keys to the property have been posted through their letterbox, without a note, just in envelope addressed 'keys ... property address' in what looks like tenant's handwriting. As we now have the keys, can we take possession?

We have today entered the property to check it is safe &secure - it is filthy, litter everywhere, with no furniture except 2 bed bases (no mattresses) and lots of rubbish in back yard. Some of our possessions listed in the inventory have also disappeared. We want to change the locks, start the clean up and get council to move rubbish, but would this be a wise move prior to the Court Hearing?

In terms of rent owed, can we continue to charge rent up to 21st September (when the Section 21 expires) if we start the clean up process?

Any advice would be much appreciated. Thanks.