By Seamus Duff Prue Leith caused gasps and nervous laughter on The One Show when she swore live on air. The 84-year-old Great British Bake Off judge was a guest on the popular easy watching evening TV show that airs week nights on the BBC. Alex Jones, 46, and 31-year-old Roman Kemp were presiding over Friday’s edition of the show – which featured Prue along with 33-year-old singer and actor Olly Alexander. And while Prue is known for being a comforting judge on Bake Off, BBC viewers were stunned when she swore live on air. Prue was a guest on the show to promote her brand new cooking show, Pru…