The News of the world contains the following offer:

For £15 you can get a car and up to 5 people (though you
might not want quite as much ballast as that) from Dover
across to Calais for the day. You must leave after midday and be
back before 0100 the next day. Offer is open for any day
of the week until April 30 but must be booked before March
11.

Although I havent done it for a while, I understand there
are some pretty good driving roads in France (please feel
free to suggest some), so if anyone is up for it, nominate
a range of suitable dates, I'll pick the most popular one
and we can book up on 0870 600 8844 (P&O Stena).

I'd suggest a Saturday as its liable to be a late night.
We can work out a decent driving route, have dinner
somewhere nice, and head back to purchase some duty free.
Let me know what you think.

Cheers

Andy.