Frequent tornados in north western Europe? 
Could someone back up this claim (which appears in the very opening sentences of this article)? 

Tornados rarely occur above 45 degrees latitude and are most frequently observed in the US, China, India and Bangladesh. But here in northwestern Europe tornados occur only very rarely as far as I know. For example here in the Netherlands the last whirlwind that could be classified as a tornado occured some 40 years ago.
Unless this claim gets some credible backup I say it is best removed.