When completing a fire risk assessment in a small block of flats are the owners front doors in the communal corridors deemed part of that assessment 

YES. need to be FD30s fire doors with S/C.

Yes, they have an impact on the safety of relevant persons in the common areas and elsewhere in the premises.

Even a basic Type 1 Fire Risk Assessment should do this (extract from the Government Guidance):

"Type 1 – Common parts only (non-destructive) A Type 1 fire risk assessment is the basic fire risk assessment required for the purpose of satisfying the FSO. The inspection of the building is non-destructive. But, as well as considering the arrangements for means of escape and so forth, the fire risk assessment includes examination of at least a sample of flat entrance doors."

Read more at: https://www.local.gov.uk/sites/default/files/documents/fire-safety-purpose-built-04b.pdf