how many of the tourist coming to krakow are British?
Not that easy to find is it ?
I found this link, I know its about Warsaw but it does say that half the Warsaw figure is applicable to Krakow , so if you worked on that assumption and took the break down of tourists shown on this site then maybe it would give you some idea ? Not too accurate though.
tourism-review.com/article/1398-warsaw-attracted-more-tourists-than-krakow
Also , this is apparently the "Krakow tourist board's official website'. <link below>
krakow.pl/en/turystyka/
Maybe email the contact and ask if they have details or a link into Official Statistics <although I glimpsed into the 'Governments Stats' and couldn't see anything.
Hope it's of some use or that maybe someone in Poland can give you better information.
:)