New Delhi, July 10 -- LONDON - Andy Burnham, the Greater Manchester mayor who spent nearly a decade dismissed as too provincial for the very top job, will become Britain's seventh prime minister in ten years on July 20 after securing nominations from 322 of Labour's 402 MPs - a parliamentary majority assembled so quickly that his only potential challenger stepped aside before the first formal tally was published.

The nominations, disclosed Thursday, leave Burnham within a single vote of the mathematical threshold that prevents any challenger from entering the race. His last potential rival, armed forces minister Al Carns, ruled himself out late Wednesday, saying that "months of internal Labour politics isn't what the country needs." Euro...