HMO conversion requires building regs?

HMO Licensing

Hi, I have just converted a 4 story single dwelling in to 6 bedrooms which is now licensed.

The conversion involved removing chimney breasts and creating door ways through load baring walls etc.

My architect submitted the plans to building regs and when it was known it was a HMO it came under all sorts of "extra" requirements which cost me many thousands of pounds more to implement, to name a few these were things like 50-70 Mil installation on all solid exterior walls, opening mechanism to the top floor landing window to act as a smoke vent when the alarm is triggered, fire boarding on all internal stud walls including on-suits, sound proofing between all party, room walls and floors, painting the stairs in fire proof paint.

When the HMO inspectors visited they didn't care for any of these "extra" requirements as long as I had the fire boarding, doors, and fire protection system correct that’s was about it.

My question for future projects is do I have to do a conversion under building regs? Can I just do the internal alterations such as knock a wall down and put doors through, with just the minimum requirements the HMO Licensing officers want for fire and safety etc.

I realise that making internal alterations that could compromise the structure of the building need to be done correctly but it is my observation that most people do not do this type of work under building control and there isn't much building control can do about it (how do they know it wasn't like that before!)

So what’s the position here?