Stop with this fake news.Ring and ask. I had one insurer not care if it was an OEM fit in the standard air box, another wanted me to declare it.
But as many say above unless you have done other mods and mapped it, the filter will make no difference apart from make a little more noise and you may lose power... TyreRviews.co.uk did a good video on it:
We have know for generations that a K&N makes 10bhp AT LEAST on a Mini 1000, so on something proper must be, what, 150bhp?