It’s a good question, here’s my take.
Rightwing pro-Trump propaganda is accessible to English language speakers, added to which the UK has a well established and dominant rightwing press supplemented by US cable networks, particularly FOX. Also on the mix are non US/UK propaganda outlets ‘Russia Today’ being the most prominent.
Keep in mind much of the rightwing pro-Trump propaganda is disseminated online via social media, immediately accessible to English language speakers,
And then there’s the actual Trump supporters themselves. Take a look at US home grown MAGA Supporters, no need to denigrate these people more than Trump already does, but realize the UK has its fair share too.
Trump’s only offering is to make people who’ve retreated to fear and hatred feel good about themselves, that’s a message that hits home wherever there’s a bigot stroking their self affirming grievances.