I am not sure whether the tenure would make any difference here: we do not have a tenure system so it would not be a big deal for a UK university.
I am not sure why it wouldn't be a big deal for a UK university, since any university with even a passing understanding of the US system will realize that tenure is typically a higher bar than promotion at most of the better universities. Indeed, at research universities, it is much more common to see Associate Professors without tenure, than Assistant Professors with tenure, at places which decouple promotion and tenure.