If the floor level of your flat is more than 4.5m above ground level (and for most dwellings that occurs at the second floor) there must be safe method of exit in the event of a fire. This can be satisfied by an external escape but it doesn't have to be. There must a 'safe corridor' to escape down with a 30 minute fire separation between it and the rest of the house. This may involve a stairwell if your flat was custom-designed as flats or some building modifications if it was a conversion into flats of a domestic dwelling. It could involve internal fire doors fitted within the property.