 His great-nephew, Peter Dowd, is the present Labour MP for Bootle, and served as Shadow Chief Secretary to the Treasury until 2020.In 1954, Mahon was selected as parliamentary candidate for the marginal seat of Blackburn West, but the seat was abolished by redistribution prior to the 1955 general election.Almost a decade later he was selected for the "bellwether" marginal seat of Preston South, a constituency with a significant Catholic population.