Hi.
I must totally disagree with everyone who told you to contact the Council. The first port of call should be your local residential Landlords Association, who will give you information that is to the benefit of the Landlord. (Similary if you have a question about your business accounts you generally ask your own Accountant). Councils give information that is to the Councils advantage.
We own a large number of properties from the Midlands down to Cornwall, some of which are HMO's and some that are not. Previously I was Chairman of the National Federation of Residential Landlords which evolved into Local Landords Assns/NLA/RLA etc.
The rules/Laws governing what is not and what is an HMO are complex and can vary from Council to Council. For example there were already a plethora of Laws regulating HMO's which became more complex under the last Labour Government who brought in Mandatory Licensing for certian categories of HMO's and then allowed Councils to have additional Mandatory Licensing under Discretionary Licensing !!! So some Councils went for Licensing everything (but at the same time excluding their own properties !!) which of course made Landlords liable to pay expensive Licensing fees (and even more expensive Fire Protection works) to the Council and of course jobs for life for the Council staff enforcing the Regulations. Exact rules would depend upon what Regulations the Council have adopted.
If the Council have only followed the Mandatory Licensing Scheme then short answer is ...it depends upon 'how' you rent the property. Certain categories do not form an HMO. For example if you have 3 workmen and they ALL work for the same Company, came as a group (have a sigle Tenacy Agreement covering all 3), work together,will leave as a group, and are responsibile for Utility Bills as a group...then it is not a HMO. However if you have individual Tenancies starting at different times,they work for different Company's, they have their own rooms with locks on their doors preventing others from accessing their rooms ...then it will be a lower order HMO.
So Landlords can 'manoever' into certain categories (to the Landlords advantage) depending upon 'how' they let the property.
That is just an outline. If you want more info then please let me know. It can be complex. However I suggest you do join your local Landlords Association as Landlords act together as a group just like this forum, some Landlord somewhere in the Country will know the answer to a question. There are benefits from Membership of whatever Landlords Assn you join as we get exceptionally low insurance costs by bulk buying power and from paint supplies/builders merchants/Ktichen units etc
Regards