Thanks for your feedback.
Local Authority guidance states the following :
"An automatic fire detection and alarm system shall be provided to ensure early warning in the event of a fire. The actual works required in any particular case will depend on the layout of the property and are decided upon by the Council following consultation with the Fire Authority and having regard to the LACORS “Housing – Fire Safety” guidance."
Thing is, since I'm a section 257 HMO and don't currently need a licence, the EHO wont come out to view!!
So if I install a Grade D and they eventually come out when the licence is required (could be next year) and decide I need a Grade A, I will then have to pay all over again for a Grade A system.