Can anyone tell me if it's possible to get a free ride on the ferry - like as the passenger of a truck or a car?
Very difficult. You'll find it next to impossible to access either cars or trucks before they pass through the ticket barriers, and once they're in you can't access them at all.
There have been so many well-publicised incidents involving people smuggling themselves into trucks that security on the French side is extra tight.

Ticket for foot passenger is around 15 euros (from Calais, I don't know about return...), and you could possibly get some cheaper fare. So it's not worth the hassle, and risk of trouble, as #1 says.

Only with an idiot.
I take you as a passenger in my car and it turns out you have 5 kilo of heroin in your bag. Or are you planning to let me inspect your bag and all your bodily orifices?
Kathy,
Look at it from the other side: if you were driving your car onto the ferry and some stranger asked if he/she could hitch a free ride, would you do it? If you said yes, then read #3 again.
Badger

Well thanks for your replies but Yes i would do it. And i hope that maybe one day this world will be a good enough place that people don't fear other people so much. But that's ok, everyone in europe can just go on living their insular lives fearing each other and never looking anyone in the eyes and the sooner i'm out of here and back to asia the better. You could say the same for why people pick me up hitching at all - i could be an axe murderer.. but thank-fully there are still some kind-hearted people in the world who help hitchers out and thankfully there are still other people out there who hitch because when this dies out the world really will have become a place to fear. does no one believe in human goodness? and if people are not essentially good, if they are all essentially bad then this world is lost anyway and i don't care if i get killed hitching tomorrow or i die at 70 in my sleep in some cold lonely flat somewhere having always done the safe thing and not living a single day in the moment. I am not very eloquent and i can't express what i'm thinking right now but i think anyone who thinks along the same lines will know what i'm getting at and the rest of you were lost a long time ago.
so wish me luck coz i'm hitching Rennes to london tomorrow.

Kathy,
I have done some research (I'm going hitching to the continent later on this Spring, or in the summer) - there is very little info on hitching into the UK. However, that's what I have found:
There is a number of free options possible with hitching to/from the continent:
1. Eurotunnel counts the cars, not the passengers - so your best bet is to hitch a car which is going through there. However, I think, only 2 people in a lorry are allowed for free.
2. Dover-Calais/Dunkerque ferries allow 2 people in a lorry for free, and if you are travelling in a normal car the number of passengers on the ticket should match the number of passengers in the car. However, if a driver buys the ferry ticket in Dover (i.e. it's not pre-booked) he does NOT pay extra to take an extra passenger (you'll need to take your passport and go with the driver to the ticket office)
2.1. Hence you need to look out for lorries with 1 driver only or private cars which don't have a ticket yet.
2.2. If the number of passengers on the ticket does not match the number of passengers in the car, P&O (may) charge £10 for alteration.
3. Longer-distance ferries like ones from Harwich/Felixstowe allow 2 passengers in a lorry - look out for solo-driver lorries. Also, I heard they get free food on the ferry so you may be able to get a decent meal for free if you're lucky ;)
4. Avoid long-distance ferries like Hull-Zeebrugge or Portsmouth-Bilbao - they take ages, run infrequently (often overnight) and often include only the driver in the ticket price.
- To hitch from Belgian direction people say it's useful to get to Jabbeke Service Station (google it) on E40 and ask drivers (with Irish or British numberplates, perhaps) there. I am not sure about France - maybe try the last peage (toll booths) or a service station before Calais?
- To hitch to the continent, try A20 near M20 junction 11a for Eurotunnel (look here: http://en.hitchwiki.org/?title=The_Channel_Tunnel), or Maidstone Services on M20.
Some say the Ashford Truckstop is also good, but I don't know where it is :o) so can't give precise directions.
Also, on your way TO the continent, it is good to ask people for lifts on the ferry/train in the tunnel, especially if the driver you are with does not go in your direction further along. On the way back make sure you get on M20 (90% chance probably) and get at least to Maidstone Services.
Happy Hitching!
P.S. Please let me know if you find a good hitching place near Calais to hitch into the UK :)
Lnx

Good luck to all the hitchers out there - please post back to let me know how it goes. Also, does anyone know of any good lift sharing websites for getting to/around France?