"Reactionary populist in these terms means things like being anti-EU" (ok, there were some other conditions)
Then I am a reactionary populist, too (no surprises, there, then, you might say). As it happens, though there is a lot of left wing opposition to the European Union the Communist Party of Britain ran on a No2EU programme here, and the French Anti-Capitalists scuppered the Treaty on the European Union a while back.
The kind of people in the UK who are in favour of the EU are the Blair supporters, and the 'Liberal Democrats'