There is very strict legislation with regard to smoke detectors:
https://www.gov.uk/government/publications/smoke-and-carbon-monoxide-alarms-explanatory-booklet-for-landlords/the-smoke-and-carbon-monoxide-alarm-england-regulations-2015-qa-booklet-for-the-private-rented-sector-landlords-and-tenants
I suggest you start with provision of smoke detectors bearing in mind that it is likely that linked smoke/heat detector legislation will be coming in to England in the next year or so. These work on radio waves and don’t need internet.
Please be aware that the Fire Service can impose improvements on you if they are so minded and carry out a spot inspection. This happened at an Almshouse Charity in Chelmsford and cost them about Ā£80K!
Part of the FRA should have been a traffic light set of recommendations. You should seriously consider all “red” actions. I suggest a conversation with your insurers as you may find you are not covered in the event of fire if you fail to act on explicit advice.
Good luck.
Clare Heyes