Sir Keir Starmer has doubled down on his inflammatory comments on immigration as Labour backlash over the language he used grows.The prime minister’s warning that Britain is becoming a “island of strangers” as a result of migration has sparked alarm with claims that it was almost word for word as a line from Enoch Powell’s infamous “rivers of blood” speech in 1968 that whipped up a frenzy of anti-immigration hatred across the UK.