LONDON — Over the past decade, Nigel Farage has ripped political conventions apart, dictated the debate on Brexit and immigration, and driven his party into contention to win the next general election.

But now the hard-right Reform UK leader faces what may be the biggest challenge in a career suddenly engulfed by troubles.

From a far more potent rival in new Prime Minister Andy Burnham to a resurgent Tory party, pressure over his finances, and a dubious gamble on a special election, Farage and his team are feeling the heat. And their poll ratings have started to slide.