Tenants have a right to quiet enjoyment of their accommodation.
Even if the landlord gives proper notice of a visit, the tenant may still legally refuse access. If a tenant refuses access the landlord should try and find out why before resorting to legal action. It may simply be the timing of the appointment and the fact that the tenant is unable to get time off work - in which case an evening or weekend appointment could be arranged.
A formal letter before any legal action may be useful. A letter should also advise that costs would be awarded against the tenant in the event that the court made an order for access. An order would be made for an inspection on a given time and date.
Only if the tenant will not make alternative arrangements or where persistent delays occur that can compromise the ability to fulfil legal obligations should a landlord consider terminating the tenancy using the prescribed legal process or seek a court order to secure access.