AnthonyB

In most cases toilets do not require fire doors anyway and so single cubicle toilets of any type don't have self closers, larger ones have them more for ventilation control/privacy.

You are looking at the wrong register (there is more than one!) https://www.ifsm.org.uk/fra-registers/assessors/buck-anthony-charles/

I'm on the Nationally Accredited Fire Risk Assessors Register (NAFAR).

You will require Building Control approval for this work (it's not exempt as Building Regulations are not the same as Planning Permission & permitted development doesn't remove the requirement for Building Regulations compliance) As part of this a fire door will be required for Part B compliance, not sure about the step, will depend on the change of level and comes under Part M.

Yes, as long as they are owner occupiers it wouldn't be an issue as long as they accepted the risk as it would only be raised if they were doing further alterations under Building Regulations.

No, only use the manufacturer's approved anti freeze agent in the correct amount otherwise you invalidate all warranties and more importantly could degrade the foam removing it's class B capability.

As above. The FRAs would have to consider the effect of a fire in the shop on the ceiling separating it from the flats as well as it's effect on the ability to use the stair.

The version of building regulations in force at the time of build is here: https://webarchive.nationalarchives.gov.uk/20141202130432/http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADB_2000.pdf Older version of ADB required self closers in flats & certain houses, however the current approach is such that you no longer need them to the stair. However on all levels you must retain the fire doors. If you wish to sell your house without hitting problems you need to refix the missing doors, but not the self closers

The attached image summarises the guidance.

Yes!

Powder and gaseous extinguishing agents are generally accepted as non conductive on all voltages - liquid based agents have also been tested to high voltage (35,000V) but in practice are marked for up to 1000V to give safety margin.

Check with BWF/Certifire & BM TRADA who operate the certification schemes - they should be able to advise if certification is current.

Doesn't sound correct, best consult your local Fire & Rescue Service who can enforce these issues.

Yes, but they do that automatically and report if they fail (either to the control panel if an integrated network or via the coded LEDs on the fitting if self contained). Just inspect them visually (& the control panel where fitted) monthly and act on the faults indicated (if any)

As your posting was delayed I believe we have all answered you sufficiently on FireNet. Fire door blanks are often used when not required, it can be for matching purposes, economy of scale on bulk buying the same blank, to increase contract value and much more!