My dad (65) is looking at getting a new or most likely second hand bike to do some cross country trails with me in the cotswolds but then also fit slick tyres and do some touring riding.
I cannot imagine his budget is very high at all. £500? so second hand, what do you think could be bought at that price?
I was thinking along the lines of inbred with rack mounts? other options?

I'd go for Specialized Rockhopper in the sales if you can get one around that price

65 – he'll like a Pompino with a 5 speed Sturmey-Archer hub and cross tyres.

I may be selling my 2010 Rockhopper in the next couple of weeks if you're interested.

yup inbred is a good choice,
not because it's a stw favourite,
but for touring a steel frame is recommended,
you wouldn't want to damage an ali frame in the middle of nowhere,
whereas you'll always find someone that would be able to bodge a weld on a steel frame.

are rack mounts vital for touring?