Mickleham Village Hall, to be exact, CV
And it rained there sometime between 4 and 5 - I know because I was outside having my picture taken at the time.
Crepeys, I wore my (smartest) jeans and db said that when sil was angsting about what to wear, he said "Not to worry, we'll never be scruffier than Stropps and her dh". In fact, we were out-scruffed by some of the cousins.
The only people wearing dresses were the old ladies. Who were, frankly, legion. Oh and a cousin who was making a speech also wore a dress.
The dcs had a great time meeting lots of new-to-them cousins. Even dd was seen to crack the odd smile, especially when she found a step-cousin her own age with similar interests. I re-found some v. funny and irreverent people I hadn't seen for a couple of decades and we made plans to see each other again soon. And I managed to more or less completely avoid the less likeable individuals.
The cousin with Hodgkins - son of the party hosts - has just had a clear scan following his final chemo. So this was most excellent news and everyone was v. happy.
It was all better than I thought it would be. And dh would like me to tell you that he was nice to me all the way there and did his best to boost my confidence - even though I shouted at him for most of the journey. 
As a footnote: all of the under-10s were entertained for the entire party in a separate room by minders. They had a fab time. They were not seen and not heard. I thought this was a bit OTT when my aunt sounded me out when she was party-planning, but actually it was blardy fab.