Only the British.You also have to remember, many people are now restricted to 90 days… meandering back is less attractive now too.
My experience over the last couple of years is by far the largest group of European campers are the Germans, with the Dutch a close second.,
The French, Scandaholigans and Italians all outnumber the UK vehicles. (Except certain sites in Spain)
Travelling last May-July it was 3 weeks before we met our first British van and on several sites we were the first UK vehicle of the year.
On a second trip travelling in August in the Netherlands, I don't remember a single UK van on any of the sites.
It would be interesting to know from the ferry companies and eurostar the number of motorhomes and caravans they moved across the channel last year.