Hi tyneside2,
The community insurance only covers the common elements of the building and urbanisation, as well as liability. The communal areas and external parts are covered but not inside your property. e.g. if a neighbour has a flood which damages your apartment this will not be covered unless it was caused by a communal pipe - i.e. the neighbour had not left the bath running and forgot about it!
When taking a mortgage to purchase a property all banks will insist on a seperate buildings policy and indeed will not complete at the notary without it.