London - Paris - Nice but what in between???

With only two days in Nice, I would skip Cannes. If you want to a day trip consider Antibes, or Villa Ephrussi and Cap Ferat.

So if I'm reading this correctly, only a day and a half in London. IMHO short changing one of the most exciting cities on the planet if the answer is yes.

Trust you are renting your car at Heathrow. Easy to do and a better way to drive out to " the countryside." Any interest in the Cotswolds villages? Wales? Oxford? The Lake District?

Or do you seek the villages shown on Mid Summer Murders?

What are your interests? History? Castles? Art? Shopping? Hiking? Photography?

Provide a bit more info and I know posters will most certainly offer suggestions, including me.

I'd see Durham.

I'd travel to the Cotswalds. We did that after landing in London a few years ago. We stopped at Oxford University to see it (just something I'd always wanted to do), and then ended up in one of the little towns Rick recommends.

Outside of Paris you have several options, and for me, zero of them would include Versailles (unless you're going in winter or unless you love crowds of people taking pictures and blocking doorways. Since you're going in July I'd definitely enjoy looking at it on the internet and do something else. My personal opinion only.) But I digress...

From Paris, go north to Mont St. Michele and the coast to see the WWII memorials. Or....Go south west to the gorgeous Loire Valley. There's a B&B where you can stay right on the grounds of Chateau Chambord. Or you could stay in Amboise, a lovely town with its own chateau but also near Chateau de Chenonceau (about 20 minutes away by car), which is one of the most beautiful chateaux, in my opinion.

I've done the Riviera and Provence and if you have a few extra days, would give a personal recommendation for Arles or Avingnon with a stop at the amazing Roman aqueduct of Pont du Gard. If it's hot, you can even float in the river there. (Not sure where the canoes are for rental but saw several people in them. It's just a gorgeous location.) We loved visiting Arles - it was a nice break from the perfect cobblestones and medieval style of other towns. It's grittier but really great - it has a Roman amphitheater that's still in use for bull games (not so much bull fights) - where razetours (young men who are thrill seekers) try to remove rings from a bull's horn. Pretty sure the audience was cheering for the bull when we were there. No animals are harmed and it's loads of fun and thick with culture.

Have fun!

I also think you should use your "extra" time in London, Paris, and Nice.

There's really nothing else you could do, with the time that you have, that would be better.

In your itinerary you need to take summer traffic into consideration. Avoid leaving a city on a Friday or driving toward a capital city on a Sunday. The roads will be jammed.

I agree with Adam that you should spend the time in Paris or along the coast using Nice as your base. Can't get better than that. Since it seems you don't want to spend much time in the large cities, you should tack the time onto the Riviera.

Actually your itinerary is very unclear and a bit disjointed. You need to count by nights and for every two nights in a place, that's only 1-1.5 days. When is the train to Paris, the 16th or 17th? This is how I read it so far, so please clarify:

London 2 nights
Countryside 2 nights
London 1 night before catching the train
Paris 3 nights
Open 2 nights--IMHO add these onto Nice
Nice 2 nights
London airport 1 night

If you don't want to see London, you should pick up the car at the airport and take off. Then to travel to Paris, drop the car off outside London and take public transportation to the train station. I would have just dropped the car back at the airport and flown instead of dealing with going back into London for a train. Then, yes, fly Nice back to the London airport the night before.
Or go to the countryside first and then into London for two nights before taking the train to Paris.

12-Jul 11:10. Arrive in London.
Pick up car for SE England - Brighton
13-Jul SE England - Hastings/Rye
14-Jul SE England - Hastings/Rye
15-Jul SE England - Canterbury
16-Jul Eurostar from Ashford to Paris (4N)
17-Jul Paris
18-Jul Paris
19-Jul Paris - day to Versailles
20-Jul TGV to Nice (3N)
21-Jul Nice
22-Jul Nice
23-Jul Fly to London (2N)
24-Jul London
25-Jul Fly back to Orlando

Sightseeing options in SE England ...
•Brighton Pavilion
•Nymans Garden
•Alfriston Clergy House
•Beachy Head (White Cliffs)
•Eastbourne Pier
•Battle (of Hastings site)
•Batemans House
•Bodiam Castle
•Great Dixter Garden
•Dover Castle
•Turner Margate
•Canterbury Cathedral
•Sissinghurst Garden
•Leeds Castle