I am going to buy a maisonette which doesn't required fire risk assessment. I was been told that as property have front door with communal garden so doesn't need one.

Sorry, and your question is .............

Single domestic premises are exempt from The Regulatory Reform (Fire Safety) Order 2005, so houses, flats and maisonettes are exempt but any areas used in common are subject to the legislation like corridors, staircases and any rooms used in common and require a Fire Risk Assessment for those areas.