I think there is a good chance this is a replica:
1. the weight is low (the one known original is 9.7 gr. https://www.numisbids.com/sale/2277/lot/?lot=401 )
2. the reverse details do not match (the small wing feathers between the large ones are too thick, the lettering is not broad enough, the numerals are slightly different).

Maybe we have a collector of modern Poland coins who knows if there is a replica like this in the market.
You could also send your pictures to an expert like Mr. Kondrat at WCN: moneta@wcn.pl
Presumably you did not pay 10,000 GBP for it, which is the value of a real one.