The Radom 1935 is actually a modified Colt Model 1911, not derived from the BHP, with which it has little in common. It is, nonetheless, not really a "copy" of anything; it is a pure Polish design. Stories that it was designed by FN or by engineers from FN are pure myth.
Now comes the interesting part. The PWU marking was not on the production pistols, only on prototypes. That one appears to be a test prototype, made BEFORE the Polish cavalry insisted on installation of a hammer lowering lever. According to what I have read, only one is known to be in existence; if that gun is not it, then there are two and they are very rare. Unlike other guns, no large number of test guns were made; only the one or two.
FWIW, the gun bears every indication of a prototype and appears to have been put through tests, one of which was immersing the gun in water.
It is not nickel or stainless steel, it is bare carbon steel, common for a prototype when there was no point in finishing and bluing the gun. The only jarring note is the grips, which appear to be standard production grips, but they could have been added later.
There is another possibility, raised by the serial number which is too high for a prototype. It could be a pre-occupation frame, with an early slide installed, perhaps built out of the scrap bin in the desperate days of the Polish revolt against the Germans.
Either way, it is truly an interesting gun.
Jim