Answers to many of these questions are really personal choice. I should say my comments are a little dated as the last time I was there was in the late 90's when I lived there.

To the questions

1. busy day-trips are really a matter of personal preference. You will miss the commentary from the tour guild. These type of day trips are the things I often do on holiday. If you drive automatic transmission cars, I would recommend that you reserve one well in advance. The typical rental is a manual transmission.

2. When I was there that would have been my choice if I was heading to the west country. nb that I was usually doing the opposite. That is driving in an parking at Heathrow and taking the tube.

3. When I was in England you did not really have to book Stonehenge in advance. However, be careful about opening hours. Mid October last year the site closed at 16:00. In mid-March that will extend to 18:00. I would check in advance as to the opening hours of StoneHenge.

As to the route, the thing to remember that the M roads are the quickest, followed by A roads in general. While you can still go 60mph on the smaller roads outside of towns, they can be more challenging to navigate.

Are you missing something great? There are many other sites worth seeing in that end of the country. One instance, Salisbury Cathedral. This is not far from Stonehenge. Another is Longleat park at Avebury [be careful with a car at Longleat]. However, on busy day-trips one does have to choose what to see and what not to see.

dooble

Only MHO, but I would not bother going to Bath just for lunch. One of the best things in Bath are the fabulous Roman baths and they take at least an hour or two to see. A historical tour of Bath is extremely interesting and that takes a couple of hours. The beautiful Abby is also worth while. Bath needs a day.

Some of the above is a little out of date or misleading.

"When I was in England you did not really have to book Stonehenge in advance."

One still doesn't need to book Stonehenge in advance but what phpacha is asking about is 'Inner Access', which must be booked well ahead.

"While you can still go 60mph on the smaller roads outside of towns,"

Be very careful w/ that. There are speed cameras everywhere.

phpacha: Your plan is certainly doable - mainly because you wouldn't be visiting the stones until after closing time. Otherwise it would be too much in too little time. Avebury is a great first stop. Then on to Bath.

Your main problem is driving in Bath can be very difficult. Even many locals don't bother - they use the park&ride lots on the outskirts. Parking there and taking a bus into the city center.

From Bath to Stonehenge takes 60 minutes on a good day. And you'll have to build in time to get from the center to the park&ride. Unfortunately can't be late to Stonehenge and you won't know if it is a 'good day' until you have arrived at the stones.

So if you do this be sure to leave Bath by 4PM. You may end up w/ time to kill at Stonehenge -but better that than being late.

Avebury to Bath takes about an hour so you'll have maybe 4.5-ish hours free in Bath.

didn't see Sassafrass' post - and he is certainly correct that Bath really needs a full day. But IF you understand you will have enough time to visit the Baths and have lunch and nothing much else - then your plan is doable

If you want Stone Circle Access, book it now. We are going in late September and there was only very early morning (6:45am) availability on a few days. I was also told there is no inner access in October. We did the evening access in summer 2006 and it was a very special way to see Stonehenge.

janisj

I agree with you that they have speed cameras everywhere. A single carriageway has a speed limit of 60mph for a normal car. This does reduce greatly in towns where the limit much lower and where most of the cameras are.

I misunderstood the OP in that I thought they were giving up on the "inside the circle". I would agree that would need to book for this.

Bath could take a day .. or two for some. Or you can pick a couple things to see. Doing a busy day quick trips really makes you decide what you actually want to see and what you want to skip.

and I would agree with janisj on the variability of travel times based on traffic or weather. On single carriageways you can get backups for a number of reasons.

Great info here! Thank you all.

We're prepared to see Bath in a superficial way, as our main goal is Stonehenge, but I think this way is better than don't see it at all.

I think the only problem now is that we may not be able to get the inner circle access in the evening (as castlevisitor mentioned), which is available in fewer dates and times. In that case, this itinerary is doable in reverse? That is to say, leave London real early, go directly to Stonehenge (to be there by 8:00 or 06:45 AM) and then Bath and Avebury? I know it would be challenging get in the road so early, but is it doable?

If you just want a nice place for lunch consider skipping bath (as you said the visit would be superficial anyways) and heading to Salisbury. This is a lovely Market town with a great cathedral with a copy of the magna carta. There are some good pubs for lunch as well. It's also very close to Stonehenge so you wouldn't have the traffic concerns.

Enjoy!