I would add two thermal curtain panels but not at the very top, instead just above the top hinge. You will still get some light and weather protection, too.

Thank you, I will give that some thought.

Check into "swing away" rods. This is a set of two rods, hinged in the outside corners of the wall, that allow the drapery panels to be flat on the door , then swing into the room to open the drape. This will work only if you have the wall space for the panels to stack against.
Another idea is to go with a single drapery panel on a decorative rod that will draw to the right (hinge side). Do not use a rod pocket or tab top drape as they take too much stacking room. Use a panel that is almost flat when drawn across door, with rings that slide easily on the rod.

I would skip a curtain altogether and do a window treatment directly to the window itsself. its less bulky and doesn't hide the interesting element of the odd shaped window. There are several easy ways to do this. One would be to cover the window with frosted translucent contact paper. There are like, a million choices for patterns and it will let light in, but no one will be able to see inside, and when its time for a change, it just peels off. Judging by the offwhite of the doorway, this might be the sleekest, subtlest option. But if you want to go colorful with it, you can also mix food coloring with mod podge and paint it on the windows, creating a mottled, stained glass effect. This is may not be your style, but again, it lets light in without letting people see inside.

I am not sure if there is a typo in your original description but I think you indicated that you need "Draft" proofing (if not then I am not sure what draught proofing is). Is that right? If that is the case then you would need a drape that would cover the areas where cold can seep in--- yes? If that is the case, I would go with a drape mounted above door alcove with a "one way draw" to the left. Have the drape interlined with bump cloth for extra insulation. The other alternative would be to beef up the weatherstripping around the door and/or add a storm door over the main door as an added layer of protection.

Thank you, Bonnie for your ideas. 'Draught' is English spelling of 'draft'! We have a listed building and so we can't change the exterior appearance at all. I think the "one way draw" is the way to go.

It looks like a really interesting piece of property! Sorry about saying there was a typo...my ignorance. Best of luck!

If you are experiencing a draught, would it not be better to see about adding weather stripping? Check by using a flashlight outside the door to find where the seal is not good. A curtain is a good idea, but you really want to stop the air, not just hinder it.

I would put custom 2-1/2" plantation shutters right on the door (of course if that would not break any exterior rules). Then I would trim out the sides with nice decorative trim - a good trim carpenter should be able to handle the arch without any problems (If they even act like it is a problem them find another carpenter). Keep in mind custom plantation shutters can be painted any color under the sun to match your existing door or trim.

If you need draft proofing then a window mounted treatment will not work. Most effective to cover the whole area.
Grommet top panels or flat panels on rings stack back quite well. If you install a rod 6-8" above door then you can also install a single hold back level with the top of the door to loop the drape behind.

What a very cool door. I agree with Bonnie's ideas, and definitely interline.

I like these