Funnily enough if you look for this policy, there's lots of references to their story, but little else, which clearly is odd for something they imply is a manifesto promise.
From Feb 24 "But by 2023, Labour confirmed it had no plans to raise the DST, and insisted the hike was only ever proposed as a “temporary measure”, according to the Times."
https://www.cityam.com/u-turn-if-you-want-to-five-financial-policies-keir-starmer-has-scrapped-as-labour-leader/
As per here https://home.treasury.gov/news/press-releases/jy2098
And here https://archive.is/sBlXS
The US threatened retaliatory action.
Thankfully someone found the links for me