1 Day tour to Stonehedge from London.

You can easily make your own way via train (if you are talking about some kind of escorted tour).

Also it’s a henge. Not a hedge. Stonehenge.

Unless these are must see sights for you I don’t recommend trying to do a day trip combo. To me you are shortchanging both locations. I know companies offer these trips but that doesn’t mean it’s a good idea, lol!!

My opinion only….

On your other thread/question titled "Salisbury", it seemed as though you were going to be staying in Salisbury overnight? Or perhaps for 2 nights? Because you were asking for all kinds of things to do--enough to fill a day or two.
I do hope that is the case; otherwise, you just won't have enough time in this area.

https://community.ricksteves.com/travel-forum/england/salisbury-9f132281-b063-4588-b38d-4da23500ae9f

Stonehenge is right outside of Salisbury.
On your other thread, I have given you instructions for how to take the Stonehenge Bus from the center of Salisbury a short distance to Stonehenge.

This makes an additional day trip to Stonehenge from London totally unnecessary.
Stonehenge is NOT near London.

You would be wise to stay 2 nights in Salisbury (and see Stonehenge) and 2 nights in Bath if you wish to see those places.
London is great, but I like Salisbury and Bath more.
The two places you asked about would NOT be adequately seen on a day trip that covers both.

To answer your question: Yes, such tours are easy to find.
Yes, you can book them online a day or two in advance.
Look at Premium Tours or Evan Evans websites.

For many tourists, the frantic pace to line up several sights per day ends up NOT being very satisfying. It is just a quick glimpse. A better experience can be had by leaving London, booking a hotel for 2 nights in another town, and just experiencing that place fully.

Thanks Rebecca and everyone, I plan to spend 2 nights in Salisbury. Happy to know all your info