The British public is more liable to laugh at a passionate politician than want to follow him or her. We are all too ironic for that now maybe.
I think most people just have total disdain for the idea of "a politician." Are there many you can really say you
like or
trust? People are starting to realise that the system just isn't designed to help them. "There all the same" is one of my least favourite clichés, but it's becoming harder and harder to argue with. The constant anti-Labour message from the tabloid media won't have helped Starmer but he isn't helping himself very much either. I know a few young people (Labour supporters) who are very switched on politically who chose not to vote in this election. If you're not inspiring people with your policies then you have to be likeable at the very least.
For all of Trump's faults (openly xenophobic, lack of substance, the inability to string a sentence together), people liked that he was a character. He wasn't
one of those. Americans tend to like a memorable name and face. He said dozens of things that would force UK politicians to stand down, he was hated by a lot of the media (and weaponised it quite cleverly) and still managed a term as President. Frankly, I'm still shocked he lost the last election - he was very unpopular with a lot of people too, I suppose.
Basically you need someone who people are passionate enough to get behind and who can unify the majority of people, ideally someone who doesn't feel so entrenched in the system. Dennis Skinner would never have been allowed to lead the Labour Party, but I do wonder how the British public would have took to him. I know people who have met Corbyn. He's a good politician, probably a good person, but he's a bit of a bore.