Hi, Jill - if this thread is still observed years later!
I used to live at Middlesex House and came across your query whilst pointlessly browsing nostalgic memories - trying to find old sales listings and internal photos, no luck. I'm not sure when my parents bought it, but I was born there in '85 and we moved away in the early '90s. It's probably for the best that I can't see how much it may have changed internally, being very attached and very easy to attach to old homes, but if it helps . . . yes, it was a very nice place. Very much a dream home for a child and probably has forever influenced my taste for cavernous older properties with large gardens. Specifics have long since blurred except a few mental snapshots, but I remember there was a sun lounge at the rear that might have been used on good days for convalescents. We sold some of the land by the road and the buyer built a house there; at some point after we moved an area of the back garden had a similar fate, judging by google satellite maps, and the tree in the middle of the courtyard has gone. Progress is overrated. I miss that tree.
The temptation to travel 100s of miles and join the knitting club is strong but I think that'd be too much; I just wanted to say that I have fond memories of the house and I'm sure it was a good place for your great aunt to be.