UK to France

If you take a British car to the continent, you're going to have to take it back or pay a double-huge drop-off fee (even if it can be done?). Just a plain old second-country drop-off dumps your wallet. Get the car as you leave Paris - - and figure out a way to get it back to France, hopefully. Fiddle with kayak.com or carrentals.com to see what the cost differential is. My experience is that I can easily cough up the price of an extra day and beat the cost of dumping the car in another country.

John, My preference would definitely be train from London to Paris. It's not only faster, but much less of a hassle. Keep in mind that you'll need to adjust to driving on the "other" side of the road when you arrive in Paris, and you'll sitting on the right side. People from the U.K. seem to manage this well, but they get more practice. IMO, driving a UK vehicle in the traffic of Paris (or other large cities in western Europe) is going to be problematic for most North Americans. Good luck!

Pay close attention to Ed's comment. Train to Paris, but pick up the car only as you are leaving Paris. Don't even think about sightseeing by driving around Paris, which has the best metro in the world.

You would not BELIEVE the hassle and cost of taking a British hire car to France.
Roger

EuroStar all the way baby! Fast, fun and safe. On it you can eat, drink and get oh so merry.

We did Eurostar from London to Paris. Spent 4 days in Paris and then picked up rental for the rest of our trip. It happened to be All Saints Day when we left Paris, so we had minimal traffic. Have Euro coins ready for tolls.