Ferry from Calais, France to Dover, UK

You can get to Calais ferry from Paris by train, but it's not cost or time effective.
Have you thought about getting the Eurostar tran from Paris to London, and then travelling on from there, either renting a car, getting a train, or some combination?
You haven't said what you are planning to see in UK.
If you give us a bit more info, we can make more suggestions.

it sounds like you are hoping to cross the Channel by ferry as foot passengers.

Unfortunately that is not as easy as it once was.

There are three large ferry companies between Dover and Calais/Dunkirk providing passenger services, but in great measure that is for passengers in/on their vehicles - cars, motorcycles, campers, etc., as well as freight.

The three companies are Irish, DFDS, and P&O.

Only P&O provide foot passenger transportation, and only on a few of their daily crossings, and none from Dunkirk (served by DFDS and no foot passengers). They don't make it easy. In addition, the Calais and Dover train stations are quite a long way from the ships. I could go into much more detail, but let it be said that if you don't have a vehicle using Eurostar between Paris, Lille, or Brussels to London is much easier. That's the train which go through the Channel Tunnel.

Can you elaborate on your plans a bit further? Where will you go by car from Dover?

I was told today about a brand new foot ferry service from Boulogne to Dover, on a sailing ship no less.
Something very, very different. The company is called SailLink.
The vessel takes just 12 passengers and a passage costs £75, so not cheap.
Apparently the company started at Easter. Last week they had their first weather related cancellation.
If you wish you can even assist the crew.

Well I did this in reverse a few years ago, and it was challenging to say the least. I took the P&O Ferry from Dover to Calais, and unlike taking the ferry many years ago (before the Eurostar link) foot passengers are rare on the ferry and not really well accommodated. Most passengers are those who are ferrying their vehicles across the Channel.

In fact, this was quite an "adventure" since I did it alone and on a Sunday....

I took the train from London to Dover, and upon arrival was told there were no taxis to take me to the ferry terminal, and I think it was because it was a Sunday. Anyway, I ended up walking and it was about a 30 minute hike with all my luggage. I ended up in a shabby terminal lounge where I found I'd missed my scheduled ferry (having not accounted for the walk!) but I was lucky enough to get a spot on the next - and last - ferry of the day.

There were only a handful of us who were foot passengers and we were taken on a bus right into the area where they were loading the vehicles and took an elevator up to the deck. The journey itself was fine, and the whole reason I took it was for the views. I got to see the white cliffs of Dover as we sailed away, and the coast of France as we approached.

The disembarkment, though, was also kind of rough because again foot passengers were an afterthought and we got unceremoniously dumped off at the nearly deserted terminal where once again I found that taxis were not readily available on a Sunday. The train station to get to Lille - my final destination - was six miles away. It was way too far to walk with my luggage, alone, getting dark on the "rough" side of town. In all my travels in Europe, this was one of those moments where I was truly alarmed, and facing the prospect of camping out in the terminal all night by myself! Then I overheard another American woman on the phone begging a taxi to PLEASE come pick her up, and I asked if I could share it with her if they came. So I did get a taxi to the train station, where I just barely caught my train to Lille.

All this is to say that it wasn't quite what I expected, having taken the ferry many (many!) years ago as a foot passenger and remembering it being very different.

Anyway, I got where I was going, and the actual crossing was pleasant, but just make sure you have transportation to/from the terminal on each end.

PS...I'm so old, I remember taking the Hovercraft across the Channel back in the day!

I remember taking the ferry back in the day before Eurostar. Some crossings, due to the weather, were very choppy.

In those days, there was a train from Paris that went directly to the Calais docks. Today, you take a train from Paris Gare du Nord to Calais. From Calais' main station, you can get a free shuttle bus to the ferry port. It's called the Balad'in

In those days, there was a train from Paris that went directly to the
Calais docks.

Yes, that is how I remember it from 45 years ago when I first crossed the Channel. So a few years ago when I decided to take the ferry again (for old time's sake!) I expected it to be similar and it wasn't at all.

And there was no shuttle to take me to the train station in Calais when I arrived - maybe it just wasn't running on a Sunday evening. I only got a taxi by the skin of my teeth or else I would have been spending the night alone in the terminal!

I'm not sure when this was but P and O now run a special shuttle bus in Calais at times when the public bus is not running, so no need to take a taxi.
It is also nothing like 6 miles from Calais port to Calais Ville station- it is just under 3 miles. Still very inconvenient, and in an industrial area, but nothing like impossible to walk, if not pleasant.
Calais Maritime station still exists (without its platforms) as a truckers stop, near to Berth 5.
And Dover Western Docks station still exists as Dover Cruise Terminal 1 from the days of boat trains. They usually ran from Victoria, but sometimes from Charing Cross or even Cannon Street.
I still refer, from habit, to the main rail routes through Kent as BTR (Boat Train Route) 1,2 and 3.
There also used to be through trains from London to Paris via the Dover train ferry. I was never lucky enough to use that service.
Folkestone Maritime station also still exists, and has recently been restored, for other uses. Ferries to Boulogne sailed from there.
Nowadays the easiest way to do the Dover crossing is on Flixbus (from London or Manchester), by either day or night, and you get to choose which of the three ferry companies you use, depending on which departure you use.
You can also still sail from Newhaven to Dieppe for Paris, although Dieppe Maritime station has also closed, so it is now the town station you use.
East of Dover Eastern Docks (where all ferries now sail from) there is a wholly separate freight port, which I have sailed from in the past as passenger on a freight ship.
If this was before Covid the sensible passenger to Dover ferry port would have taken the near hourly National Express bus from London - which no longer runs due to lack of demand.

It is also nothing like 6 miles from Calais port to Calais Ville
station- it is just under 3 miles. Still very inconvenient, and in an
industrial area, but nothing like impossible to walk, if not pleasant.

I'm talking about the Calais-Fréthun station where I was catching the train to Lille. I just looked it up and it is EIGHT miles! So yes, way too far to walk, especially alone in the dark with all my luggage.

(PS...I don't remember exactly why - and again it may have had something to do with it being Sunday evening - but for whatever reasons I couldn't find a train to Lille from Calais Ville.)

There are many more inconveniences now to get from Calais to Dover by ferry, and my experience took place back in 1999, so quite a while ago. However, it was a wonderful trip, standing on that ferry with the wind whipping around us and watching the white cliffs of Dover approach.

I even sang The White Cliffs of Dover as we got closer, much to my daughter's horror. She pretended she didn't know me for the rest of the trip. :-) But it is a very iconic trip and I'm so glad I had the chance to experience it.

I'm also contemplating doing the Calais to Dover BO Ferry so we can see the cliffs of DOver. I'll have a Europcar rental and plan to drop it off near the ferry in Calais. Somehow get to the ferry and then pick up a Europcar in Dover to begin the UK version of our trip. If anyone has any thought/suggestions I'd welcome them.

We did the ferry trip as foot passengers several years ago. Definitely a worthwhile experience if you are an Anglophile. The rental car drop off site then was right next to the ferry port - easy walk. Just be careful you don't accidentally get into the line for cars that are boarding the ferry.