If the tenant doesn’t vacate after the possession order, to obtain possession of your property lawfully, the last stage is to apply for a warrant for possession from the court. It is not necessary in all cases, but it tries and removes your tenants without a warrant and you could face criminal charges. Some tenants cannot be re-housed in social housing without receiving the warrant.
Only court bailiffs can enforce the warrant - they will attend the property and secure it after the tenants are moved out. The bailiffs have a right of entry to undertake the eviction.