I have only just become aware of this thread, but I can confirm that Broad Aston is OO gauge. The current layout incorporates most of what was there in 1974, with Camwell Junction still capturing the atmosphere of a GW country junction station in spite of the addition of an extra siding and a dairy.
Yes, some of the country branch line feel has got lost over the years, but there are still areas of the layout where you can shut the mainline out of your sight and just enjoy the rural atmosphere.
As a number of you have commented, the layout is all about running trains from somewhere to somewhere and with a purpose. The system of using cards for freight wagons brings a whole challenge to the shunting of goods trains with each wagon having a specific destination. Having grown up with the layout, it really is a fun layout to operate and can easily absorb 7 experienced operators for a full weekend, stopping only for meals.
Sadly, there will be no more articles by HW Burchell as he died in August 2020. What will happen to Broad Aston is not certain as none of Howard’s children has an empty 10m x 4m shed. Rest assured that Tre Pol and Pen and the rest of the rolling stock will find good homes, hopefully largely together.