Complex sentence: In 1971, Mahon sought the Labour party nomination in the Liverpool Scotland by-election, the seat with the largest Irish Catholic electorate in Britain; his brother Simon Mahon was Labour MP for the adjoining seat of Bootle.
Split into simpler sentences: In 1971, Mahon sought the Labour party nomination in the Liverpool Scotland by-election, the seat with the largest Irish Catholic electorate in Britain. His brother Simon Mahon was Labour MP for the adjoining seat of Bootle.