Somewhere between 7 to 8 hours on a motorway in London, in 2011 I think. It was my (ex) partners birthday where I was treating her for a weekend away. We were staying just outside of the city.
As we were heading into London on the day of her Birthday, an accident happened a few miles ahead of us, which was around 11:30 in the morning. We became what turned into a 20+ mile tail back where nobody moved for hours. We got talking to to an older couple stuck behind us, who were heading to a friends with a home-made cake, which they let us have, so we ate that at the side of the motorway.
It wasn't until after 7pm that cars starting moving, what a shit birthday that turned out to be.