Abandonment of property

Access

I have just visited one of my properties (to undertake an inspection, having sent written notice in advance of my visit) and discovered it apparently abandoned. The front door was not locked and the rear patio door and back gate were wide open. A set of door keys to the property were left on the (landlord owned) dining table. None of the tenants’ furniture or possessions appeared to be present, apart from several airbed mattresses, 3 pairs of shoes, and a few toiletries in the bathrooms.
Question is, after a second visit this evening, with the conditions still the same, and deciding to make property secure by locking it with my own set of keys, am I allowed to effectively ‘take possession’ as it was clearly abandoned?
I have had no response from repeated messages to the tenant. The most recent rent (4-weekly) was due on 10th August and no payment was made. The next door neighbour seems to think they have left. The tenant is only into the third month of the tenancy, which was created with an initial 6-month fixed term. Thank you for any advice you can provide.