On the same £65,000 gross, a worker takes home roughly 1828 zł more per year in Poland than in United Kingdom. That gap reflects the tax structure alone — before rent, healthcare, or savings behaviour come into play.
Housing is the first multiplier. United Kingdom has high rent pressure, while Poland has moderate rent pressure. That means part of the higher take-home in Poland can be absorbed by rent if you land in a major city.
Healthcare and pensions go in the opposite direction. United Kingdom runs a universal healthcare model — NHS provides universal care funded from general taxation, with private top-ups. Poland uses a public model — NFZ public system with growing private supplements. The country with lower take-home often shifts costs that the other country leaves to your private budget.
Net-of-everything, a relocation decision should weigh strong public welfare in United Kingdom against strong public welfare in Poland, plus differences in pension capture, social safety nets, and city-level cost of living.