MANCHESTER — British Prime Minister Keir Starmer vowed on Friday to fight "the extremes in politics" after left-wing and hard-right parties both beat his ruling Labour in a crunch vote in a traditional stronghold. The embattled centrist leader called the humiliating third-place finish -- behind the victorious leftist Greens and anti-immigration Reform UK party -- in Thursday's by-election for the Manchester parliamentary seat "disappointing". Coming just weeks after defying calls within his own party to resign after a string of policy U-turns, missteps, and fall-out related choosing an ambassador to the US linked to Jeffrey Epstein, Starmer vowed to "keep on fighting" while acknowledging voters were "frustrated". The result in the constituency of Gorton and Denton that Labour has dominated for decades, shows how the centre-left party is being squeezed by both ends of the political spectrum and the country's traditional two-party system is fracturing. It also suggests that Britons are looking more towards insurgent parties for answers on long-standing, hot-button issues like the high co