I think IanT might be replying to me.
The private railway track and its model buildings are easily visible through the shrubbery to the right of the public footpath. I haven't noticed the house but it must be there somewhere, between the path and the river Thames. Just after passing the property the footpath bends right to return to the river side, towards Marsh Lock and Henley.. I first saw it about 30 years ago and a friend of mine walked past it last week, hence my renewed interest. I think that Fawley Court is a huge pile on the far side of Henley.
Never mind, it is not important; I hope that this thread about scales and gauges has been informative for others as well as me.