Most front doors are required to be fire doors (FD30S standard), particulary where they open onto a communal area. This is to give you protection for at least 30 minutes in the event of an outbreak.
The council has a scheduled programme to inspect and install fire doors. If your door needs repairing outside of this programme, you will need to contact the home ownership team.
You can only replace the front door to your property yourself if it is not a fire door. You can check this with the home ownership team, and they will give you permission to do so if it is not a fire door.