My husband and I have just moved into a rental flat which has living room/kitchen on the ground floor and 2 bedrooms down in a basement level.  Both bedrooms have double sliding doors out to a mini contained patio (5' x 4' and 9' high) covered with a metal railing on top at ground surface level.  This railing/fencing is not removable.  The landlord advises the doors and fire/smoke proof for up to 30 mins.  Obviously I'm super concerned about what to do in the event of a fire upstairs if we are downstairs.  We could exit to this mini patio but we wouldn't be able to get out from there and would rely on being rescued by the fire dept.  The other concern is that there is no mobile phone signal down there (we are looking into a signal booster to help with this problem).  

Is this legal?  Shouldn't we have at least a ladder and be able to unlock the railing from underneath?

You should have a smoke & heat alarm installation which would warn you before the route becomes untenable. How old is the building and it's conversion to current configuration?