Turns out the sleeper supplement (from the mouth of an agent at ACP Rail is $100 per person (and that's a lot more than the 38 pounds quoted above.)!>

Yes indeedy - 38 quid is about say $60 or so - i have never had trouble booking these in the U.K. but you have to IME go to either London Euston station in London or a ScotRail station in Scotland which will be fine for you and you have loads of time probably before taking the train.

Lynn - let me congratulate, not flagellate you for including your young kid in trip planner and somethings that are important to them

A family trip is just that - not for older adults to strictly ignore their 'whims', etc

so hats off to you all for that and may others learn some lessons from it!

I used a Scottish sleeper last month and the supplement is definitely £38. Any station with a booking office should be able to make the booking, though bigger stations are more likely to have experienced staff. I got the sleeper from Preston to Inverness, but booked it at London Waterloo.