Why not ? It should be possible, the UK is part of the European Union, EASA, OPS 1, JAR-145 you name it and I think Poland is the same, so equiv. standards.
This sort of leases inside community is nothing extraordinary, there are plenty of airplanes operated on another EU register, just have a look for e.g. on the Irish register, I bet half of them are operated by foreign airlines EU and non EU members. This is nothing new and standard in commercial aviation for years already. May be not much utilized in Biz aviation though.