Thanks all! I was going to start with methylated spirits (which is what I've always called them anyway despite being a Yank, it just sounds cooler), and then try brake cleaner, which Steve Perry told me to try years ago. But I've got a gallon of alcohol (which, confusingly, is also known as "white gas" here, I used to use it as fuel for my little Svea backpacking stove) in the garage so I can go ahead and strip my E.I (Early) floorboard after an ill-advised attempt to brush paint it the other night.
All best,
Dutch