My Father-in-Law was texting me saying that he called his Bank of Scotland Home Insurance and they said that not having them wouldn't affect his insurance. I advised that he get that in writing! lol
He said that there's nothing in any of the policies/documentation about any sort of smoke detectors never mind interlinked ones, but again they may change this come February and all you might get is an email or letter with an update in terms which I suspect is often ignored (kinda like the never ending bank fine print updates which keep coming in).
I also advised him to check that there's no small print about policy holders have to adhere to current regulations etc, i.e. a blanket rule.
Either way, I suspect that come a big claim and you don't have the appropriate detectors, then whether or not it's in the policy I'm quite sure they can and will use, abuse and hide behind the law. After all, insurance companies aren't exactly known for their integrity.