Scottish legislation has changed. Introduced in February 2019, the change applies to all households in Scotland and must be met by February 2021. The new Scottish legislation states that an interlinked Fire and Smoke alarm system must be fitted in a property and that there should be adequate Carbon Monoxide protection.
Scottish Government link:
https://www.gov.scot/publications/fire-and-smoke-alarms-in-scottish-homes/
Latest news:
https://www.gov.scot/news/proposed-delay-to-fire-alarm-regulations/