Can hardwood lipping be added to both the top and bottom of a door leaf? A corridor door has a gap of 35mm at the bottom and 15mm at the top. Would a new door be required or can lipping be added to close the gap?. There is no information on these doors and believe they are about 40 years old. Also the gaps on hinge /closing side are less than 2mm. Can the edges be planned slightly?

From what you say, this door appears to be a timber-based Nominal Fire Door or Notional Fire Door.  That being the case, lipping the top and bottom edges with suitable hardwood and using urea formaldehyde based adhesive would be a suitable repair. Planing the hanging edge by 1mm would also be a suitable repair. 

An alternative repair for the threshold gap could be to install a threshold plate to the floor, under the door.