Studia uzupełniające magisterskie (po licencjacie) na UE

You need to apply to the university direct if you want to do a postgraduate MSc in Linguistics or English Language. If you want to do an undergraduate course, you need to apply through UCAS. Either way, you'll have to provide evidence of your ability to communicate in English, for example IELTS.

Also, according to NARIC, the equivalent of the Polish 'licencjat' in the UK is 'BA', and 'magister' 'BA (Hons)', i.e. both at undergraduate level.