“Working alarms save lives in the event of a fire in your home you are at least four times more likely to die if there is no working smoke alarm.”

Do the regulations apply where the premises are let under an existing tenancy? Yes.

For more details: https://www.gov.uk/government/publications/smoke-and-carbon-monoxide-alarms-explanatory-booklet-for-landlords

From 1 October 2015 all landlords in England will be required to install smoke alarms on every floor of their property, and test them at the start of every tenancy.

Landlords also need to install carbon monoxide alarms in high risk rooms such as those where a solid fuel heating system is installed. Sanctions for not doing so include up to a £5,000 penalty.

http://www.landlords.org.uk/news-campaigns/news/parliament-approve-smoke-and-carbon-monoxide-alarm-england-regulations-2015-in-t