We will be in London in mid September as part of a Scotland, England and Paris trip. Has anyone any advice on how to and who to use renting a car and tour driver for a (long) one day trip to Bath and Stonehenge?
A driver might be nice, but is not necessary. As has been discussed on this forum before, there is regular bus service to Stonehenge from Bath and from the Salisbury train station. There are also day tours from London.
Frequent fast trains (125mph) trains go from London Paddington to Bath in 1 hour 15 minutes. Bath station is right in the centre of town and all the main sights are within easy walking distance. No driver will get you to Bath that fast.
https://www.seat61.com/london-to-bath-by-train.htm
If not staying in Bath or Salisbury, consider doing Stonehenge as a day trip by public transport from London. Train London Waterloo to Salisbury and then shuttle bus to the stones. On return - be sure to see Salisbury Cathedral.https://www.thestonehengetour.info/bus-timetable/
There are numerous tour companies such as Evans Evans and Golden Tours that offer one day Bath/Stonehenge tours.