Well, that was fun, thanks for everyone's suggestions.
We finally decided to stay in the B & B hotel which is right next to the stadium as transport links to the town centre are so good, and because it was £30 a night for both of us.
Lovely city, superb Metro system, great food and bars. We headed back to the hotel at 6pm on Saturday evening, ready for the 8pm kick off, and it was only then that we found out that the game had been rearranged for Sunday at 2pm. So, back to town, battle resumed...
The atmosphere outside the ground on Sunday lunchtime was intense. Lille fans were singing and chanting outside bars, casually lobbing firecracker after firecracker - I saw two guys bleeding from injuries from these. The riot police were lined up about 100 yards away, but basically let them get on with whatever they wanted to get on with. Then, suddenly, they all marched off together, towards where the Lens fans were entering the stadium, and it was like a scene from the 80s - fights, more firecrackers being thrown, police charges...
In the ground, which is a superb and beautifully designed stadium, the atmosphere was incredible - loud, non-stop, and the fans of each team clearly hate each other. Ultras are a strange phenomenon, to be honest. They never stop, and rarely react to what is going on on the pitch. It is all so choreographed - a bit like line dancing, which is fine, I suppose, if you like that sort of thing. As a neutral, they are brilliant to watch and listen to, as entertaining as the game itself.
A good game too - 44500 there, Lens took the lead, Lille won 3-1.
This was when our choice of hotel absolutely proved its worth. There was underground parking for hotel guests, but football traffic had been prevented from using it. So we were in the car five minutes after the game finished, straight onto the motorway, and back to Calais within 90 minutes of the game finishing.