I'm surprised you're reiterating surprise: you were off by two orders of magnitude, and the initial surprise only had purpose as a rhetorical device, it wasn't based on anything (why is > 10 surprising? 70M people in UK...)
Just imagined on the day of brexit whole set of islands just started drifting few hundred kms towards west (or south-west given how canary islands often feels like british overseas territory?) to underscore the leaving part.
Islands off the cost of a continent are still generally considered to belong to the continent. IE Japan is still in Asia, Cuba is still in North America, etc.
Eh - for the world's audiences: EU is not Europe. I geddit how/why why people equate eu == europe - it would simplify things for all, one niggle less to consider. But - it ain't so, for better or worse. There are countries in Europe, that can't be members of the European Union, or could be, but don't want to be members. (e.g. UK, probably Island, Switzerland, some of the Nordics) There are no countries in the European Union, that are not part of Europe. So EU <= Europe. (unsurprisingly)
Convert that to GBP and you get about £7.5 million.
Figure that the UK accounts for about 15% of the European economy and assume it contributes to Wikipedia at about an equal share.
That's about £1.125 million in estimated annual recurring contributions from the UK.
You said 10-100/mo, so let's assume £55/mo or £660/year as the mean.
That would be about 1,700 Brits, a surprising number.