Landlords of residential premises who are seeking to have tenants ousted because they have breached a condition of a suspended county court order for possession currently require the permission of the court to send in the bailiff. Without that permission, any action taken by the bailiff will be unlawful (see http://www.breakinglaw.co.uk/2017/01/suspended-possession-gone-wrong.html).
My predication is that the permission requirement will be eliminated from 1 October 2018.
Outright possession orders where no suspension has been imposed are unaffected and a request to the county court for the issue of a warrant of possession is not required. The warrant authorising the bailiff to evict will be issued on the landlord's request without prior permission.