There's a Mistletoe Cottage which is, in fact a tree house, complete with electricty I believe, which is in the grounds of Amberley Castle. Not sure but I think there is also a Mistletoe Lodge in the grounds (or it might be one and the same). Check it out on Google.
Brilliant, Christiana. Many thanks! Actually, I should have known this because I went to a wedding at Amberley House many years ago. I wondered what the Best Man meant when he said the Briegroom was out of his tree.