The following is a synopsis, full details in the thread mentioned earlier
Write a letter (getting free proof of posting) to the tenant telling them that you will be attending the property at X o'clock in 3 working days time to view it's conditon as per section 11(6) of the 1985 Landlord & Tenant Act. Tell tenant to contact you if not convenient.
If tenant does not answer the door, you are okay to enter so long as all you do is view the condition of the property, though presumably your eyes may detect whether anyone is still living there! If tenant is there but refuses entry then it becomes more complex & you may have to go away & get a court order.
You would us a similar process for repairs but in that case it would be section 15 of the 1988 Housing Act.