Let's assume that we're dealing with relatively wealthy individuals in both cases. Would they have dressed very differently? Wore their hair or facial hair in different styles?
I made a couple of quick scans from my reprint edition of Auguste Racinet: Le costume historique (1888)
14th century: Polish townspeople and noblemen. Image 1 and Image 2
For the 14th century Racinet does not distinguish England from other western European countries in the image captions. Here are a couple, from the same book. In general, Racinet is a bit vague about the exact dates and often groups together costumes generations apart in one image. Still it is easy to see the differences between the countries. In particular some of the Polish garments are of Turkish origin. As for facial hair, it looks like the Polish always had a propensity for flamboyant mustaches, although it got much more common and pronounced from the 15th century onwards (those images I have not scanned, because the question named the 14th century).
European Nobles in short robes, 14th century (This will be the more relevant image)
French Nobles, mid-14th to mid-15th century (A bit late, the heavily pleated doublets are clearly 15th century)
Sorry about the image quality, the book is a big folio which my scanner can't handle.
EDIT: Added material from other post below.
Your time scale leaves this a bit of an open question. By the 17th century and the rise of Sarmatism in Poland, the difference would likely have been obvious, with the Poles wearing "oriental" style clothes and likely having the notable Polish noble hairstyle (basically a shaved mullet) and impressive mustache. (See Theorem Egregium's image 1, which gives a hint of that style on the second fellow from the right.)