Focusing so strongly on immigration and related issues only strengthens Farage. It does nothing to convince the die-hard Reform people and alienates your own voters. We're already seeing Labour split to a new party (well, assuming it doesn't implode in classic left-wing infighting). It's lose-lose.
Labour won 2/3rd of MPs with just 1/3rd of the vote, the biggest gap between MPs and vote share in modern history by quite a margin. In many ways they "lost" last year's election because that's a very underwhelming result after running against a deeply unpopular government that's been in government for almost 15 years. They've been on a thin ice since day one.
All of this is such an obvious mistake that I truly don't understand what Starmer is even thinking.