Newark Park visit - 15th August
We visited the National Trust's Newark Park on 15th August as this is now the agreed destination for the mirror/s. It's in a beautiful setting, and this is what it looks like:
It was built in the Tudor period but is very much late C20th inside. There are lots of potentail stories, going back to the bloke who had it built, Nicholas Poyntz:

The house was built from stones taken from Kingswood Abbey after it was 'dissolved' by Henry VIII. So, one possible set of characters for the mirror would be disguntled monks, especially as this was a bit of a party place for Poyntz.
There are numerous oil paintings around the house:

Some of which have glass in front, making them a bit mirror-like:

We may use this as a guide for style when it comes to filming. Another possible set of characters is three young Tudor women who have been watching the hunting in the park below from the rooftop, and are now excited about the men coming home. There would be two possible locations for the mirror - one on the first floor, by the stairs, instead of the oil painting on the left here:

The other would be on the top floor by a bedroom door, instead of the painting (cupboard doors would be shut):


The final idea for a character is James Power-Clutterbuck the son of the last owner, who was in the Royal Flying Corps and was shot down by the Red Baron in 1917. A mournful character, perhaps, thinking of how the house would have been had he lived.