What makes you think so in England?
I'm not a landlord and I've not helped anyone who is with the regs since
2014. But I saw nothing in the new regs in 2015 to require interlinked mains alarms in non-HMO properties and can't see anything in the current guidance on gov.uk or from my council.I also don't know of any legislation that applies to _existing_ properties, when rented, the higher standards for new builds in the current Building Regs. But that's not saying a lot given the length and width and height and depth of my ignorance.
I don't know what the Scots do and don't accept.