can he somehow transfer his skills so he can work as a Certified Electrician in the UK (using his Polish-obtained qualification)? Hope that makes sense?
Maybe in the long term but I shouldn't think it would be easy in the short term. The UK has strict regulations for anything to do with electricity wiring/rewiring nowadays. Every installation has to be certified by a qualified electrician who can certify he or she knows all the British wiring regulations etc, and has completed the right exams to prove this.
It would be unfair to expect someone from a foreign country to know all these regulations straight away and for safety reasons there would have to be some type of test. Electricity is a dangerous necessity and sometimes even professional electricians can get it wrong. Just a few months ago in my city, a young plumber was electrocuted plumbing in a new washing machine. He was found dead beside the machine which was wired by an electrician shortly before, and unbelievably he had two wires connected to the wrong terminals leaving electricity flowing through the metal casing of the machine.
Your friend is probably a very competent electrician in Poland, but may still have have to sit an exam to prove he is competent with British wiring regulations.