Complex sentence: Many towns and cities in the UK have long established and relatively large Polish communities, most notably London, Liverpool, Birmingham, Bradford, Huddersfield, Leeds, Manchester, Nottingham and Wakefield.
Split into simpler sentences: Many towns and cities in the UK have long established and relatively large Polish communities. Besides London, already mentioned, there are significant Polish communities in Liverpool, Birmingham, Bradford, Huddersfield, Leeds, Manchester, Nottingham and Wakefield.