Well fuck me you are correct.
“The Romans wrote about growing wine grapes in Britain in the first century,” says Avery, “and then it got too cold during the Dark Ages. Ancient tax records show the Britons grew their own wine grapes in the 11th century, during the Medieval Warming, and then it got too cold during the Little Ice Age.

I admit when I learned that there were none was in the early 1960's (even then it may not have been completely correct as there are reportedly about 500 now!
The late 1950's saw the last time the River Thames froze over.