Driving from Paris to London - with a dog!

Not sure how to help you with this. Is it possible to take the dog on the train? If it's a service dog - you should be able to get on a train. Try the Eurostar. Good Luck!

Have not done this but maybe a ferry from France to UK? It might be another option.

Elizabeth, take a look at this page on The Man in Seat 61 website for lots of information about travelling between France and the UK with a dog. Many people take their pets back and forth across the channel all the time. It's easy with your own car, which you either take on a ferry or on the EuroTunnel (see this page), but The Man in Seat 61 also talks about other options.

For people with guide dogs (which is the British name for what I think you might call "seeing eye dogs") the Eurostar is a good option. You would need to make enquiries with Eurostar to check whether they would regard your service dog as a guide dog, and thus permitted on their trains.

Any one-way rental will be costly. There is a huge drop-off for renting in one country and returning in another.

Assistance dogs with recognised accreditation records can travel in the cabin to/from/in the UK. Not clear if you have checked out this possibility.

Thanks for the information y'all! Flying into London requires pre clearance, which can take up to two months, and I've not received a response from the folks at Heathrow who would do the processing. Rental fees are exorbitant ($2019 one way!), and we'll have a ton of luggage as well, so it look like we'll do the taxi service. Man in seat 61 website has great ideas, thanks again!

Cunard's QM2 allows dogs in a special kennel on the top deck and has transatlantic sailings from NYC to Southampton. On a recent Holland America cruise I took there was a woman with a service dog which seemed to accompany her everywhere except to the dining room. Cunard may have a similar policy for service dogs and your "ton of luggage" would be more easily accommodated as well.

Here's a New York Times article written by someone else who relocated to London with a dog. It mentions that kennel space on the Queen Mary is booked up a year in advance: article link

I assume you are aware that taking any animal into Britain, regardless of mode of transport, involves a lengthy process and paperwork that needs to filled out well in advance of the Trip? You will also need to pass through passport control/immigration on entry to the UK wether you arrive by Air, Train, or Car/Ferry.