Dear Charles, It would probably look less 'amended' if you added to the frame rather than the door. Add equal sized timbers on the sides of 32mm each and 24mm to the top. Any good Timber merchant can supply you with cut, planed wood, just makesure it's Hardwood for longevity.

Thanks for your response. The only problem would be making the entrance smaller which could lead to problems removing furniture etc. in the future. I understand that by adding to the door, with hardwood, it may swell.

I have done similar in the past with an internal door (it was one with stained glass at the top, a bargain even if it didn't fit) If you are handy with a plane then it should be possible. I would recommend stripping all the paint off the door before you start. When you add the wood strips use a good external quality wood glue and sash cramp them to the door. I would recommend that you go slightly oversize and plane down rather than try for an exact fit straight away. Once you have got it to size, drill and screw through the strip and into the door for additional strength, also making sure that any hinge and lock screws go far enough to get into the original door. A decent external filler over the joins sanded down and then paint.

Great, that should save me some brass!