Just to flag up that whilst it is meant to be set in the Cotswolds, it is mostly filmed in the Chiltern Hills in Buckinghamshire and South Oxfordshire, which is closer to London and more accessible than the Cotswolds. I would try to identify filming locations from the internet, make a list and then look find a black cab (I.e. licensed London taxi) driver who would be prepared to do a 1 day tour - just google black cab tours or similar. Lots of London cab drivers are willing to do this sort of thing for a fixed price, and your parents will be safe and looked after.