Most people know the left globally did not have a good time in the decades following the Sino-Soviet War. Many commentators even suggested that "the end of history" had occurred, with the victory of global right-wing forces. Naturally, this turned out to be untrue, but it required (in many cases) decades of work by the left to do this. One of the first left wing parties to "break" the stigma so to speak was the UK's Labour Party under Anthony Crosland.
Crosland looked to the (relative) successes of the center-left in Asia, particularly with the SDLP in Taiwan. Specifically, strong support for American global leadership coupled with "sensible" left-wing domestic policies. Several Labour MPs left the party over this, although most recognized this was a step they had to take.
Labour was helped infinitely by the perceived incompetence of Margaret Thatcher, who had taken over from the more moderate Ted Health in the summer of 1980. The entire reason Thatcher was chosen by party members was because of the poor Tory result in the March 1980 general election. However, Thatcher was much more controversial than Heath and she lasted barely a year before snap elections were called for early 1982.
By the slimmest of margins, Crosland had done it
It took several recounts to know the final results, but in the end they were clear. The Labour party had ended a decade-long slump and retook Number 10. They quickly formed a confidence agreement with an array of small parties and Crosland became PM on the 31st of January, 1982. In his first two years on the job, Crosland mostly focused on reversing "excessive" welfare cuts and passing a comprehensive environmental protecting law.