By Andrew MacAskill, Elizabeth Piper and Alistair Smout LONDON (Reuters) -British Prime Minister Keir Starmer won a vote on his welfare plans on Tuesday but it came with a significant political cost as he suffered the biggest parliamentary rebellion of his premiership and backed down on key elements of the package to secure the bill's passage.

British Prime Minister Keir Starmer marks a year in office this week, facing challenges from within his party and the public.

Sir Keir Starmer’s government has gutted its welfare reform legislation hours before a crunch vote, in a U-turn that means the package is likely to make close to zero savings.