Planning Permission

HMO Licensing

This is an urgent request for information concerning whether or not planning permission for change of use from a residential property to an HMO.
I am owner occupier of a licensed HMO and have just been asked to provide written confirmation to this effect.
I have been advised by the local council that despite the fact that my property has been an HMO for some years prior to the change in the law last April I do in fact need planning permission.
However upon asking two professional people they disagree and tell me this isn't necessary.