I own a ground floor flat and rent it out. It is in a block of 4, 2 up and 2 down.  I have a back door into my garden and a front door into a communal hall/stair.  My front door is next to one main entrance door, stairs in the middle and another main entrance door on the otherside of corridor going out (therefore 2 communal escape routes).  Do I need a fire door on my front door as anyone in the flats could access the other escape door without coming near my door and vise versa.  Also both upper flats have balconies.

Yes to stop a fire in your flat preventing escape through the internal common stair and likewise making fire fighter access difficult. Flat front doors are primarily to protect others not the flat on fire.

Whoever is the freeholder (or the TMC if all the flat owners share it) should have carried out a Fire Risk Assessment which, if suitable & sufficient, should have considered this, it's been a legal requirement for 15 years!