The fire regulations for the communal areas of flats falls under the Regulatory Reform (Fire Safety) Order 2005, Building Safety Bill and Fire Safety Act 2021 which is due to come into force soon.
The requirement is for the responsible person to carry out a fire risk assessment for the communal areas which should ensure that the flat entrance doors are fire resisting and have self-closing devices.
Each flat should have mains-wired smoke detection. The requirement for a fire detection system in the communal areas depends on whether the flats are converted or purpose-built. It also depends on the number of floors and flats in the building and number of escape staircases.
The fire risk assessment for the communal areas will include all flat entrance doors (although generally speaking only one-two doors need to be checked) so the cost can be shared between all tenants/landlords etc.
For all residential fire risk assessments please enquire here:
https://www.whalefire.co.uk/residential-fire-risk-assessments.aspx
For all London fire risk assessments, please visit here:
https://www.whalefire.co.uk/london/fire-risk-assessments-london.aspx