We drove from Rome. 17hr to Calais
You need a hire car registered in the country you intend to leave it, otherwise a BIG charge may apply. Ask specifically for this at the hire places. (our basic was 400 euros for 48hr hire dropping off in france but they said an italian car left in france would be at least another 700-800 eu)
If you go to an airport or big city hire place and are lucky enough to find a Fr or UK car I reckon you could find passengers quite easily (or go there to become passengers). These cars will sell as soon as they become available so you'll have to be persistent/lucky
If changing countries, DO NOT believe anyone who tells you a big charge won't apply for the "wrong" registered car, get this in writing instead (or record on a phone?). We were told no charge under the circumstances to leave a Fr car in UK, confirmed this again, took supervisor's name and then were asked for a massive extra payment when we arrived (still sorting this out & making slow progress)
Ferries weren't taking foot passengers when we tried to cross (WTF ??) though I heard Sea France are now doing so on stand-by basis. If you don't get a UK hire car, maybe someone could ferry across to france and then bring you back - prob 2 separate 1-way bookings?
We have had our return flight cancelled and are now having to wait until tomorrow 1pm for news of when the next flights will/if be leaving. 
when i get back.
