Once I had got past the queues on the Oxford ring road, the M40 wasn't too bad (though not at its fastest), except that it decided to start raining heavily. But just before junction 15 there was a sign saying `accident after J16'. For various reasons I didn't leave the motorway, which turns out to have been a mistake (though if I had, I might have spent two hours being lost instead of stuck in traffic). Things seemed OK for a while. I had already passed a flashing sign saying `50', then I passed another saying '30', and then things ground to a complete halt.
After a while of crawling at a snail's pace I looked at the map to see how close I was to the next junction and whether I could find my way from there - and it was only then that I saw just how far away the next junction was. So it was a very long time before I passed what was probably junction 16 - and didn't leave the motorway because there was no exit there! Fortunately it wasn't long after that that I passed the (presumed) site of the accident where there was just a police car in the right-hand lane, and the traffic started moving again.
The centre of Solihull is a bit of a maze, but miraculously I found my way into John Lewis car park as previously arranged - by which time it was almost 7:30. Thursdays is late-night opening, which means that everything closes at 8pm. This to me does not mean `late night' for a large shopping centre. But anyway, there was little time to do anything except pick up bopeepsheep and smallclanger and transfer the bags before driving out and paying £1 for the privilege [this is a car park attached to a large retail complex, so naturally you have to pay for parking - and even though 0-1 hour is listed as 70p it charges a flat rate of £1 after 6pm].
But we made it back to Oxford in less than 90 minutes (noting that the other side of the motorway was still fairly jammed).