Boris Johnson has launched a scathing attack on Andy Burnham after announcing his plans to run for the Labour leadership, branding him a "Mancunian mystery".Sitting down with GB News Political Editor Christopher Hope, the ex-Prime Minister declared the country "doesn't know what he stands for".Asked if he had "any advice" for the newly elected Makerfield MP, Mr Johnson told GB News: "Yes, get things done quickly. You have no honeymoon, not that …