My school (not U.K.) had: mandatory mask wearing for everyone, one way systems, designated year group bubbles for lunch & break, PE uniform worn on PE days to avoid changing, hand sanitizer everywhere, temperature checks before access to campus was allowed - U.K. schools could do most of that.
We also had - & these aren't realistic in many U.K. schools - huge classrooms & small teaching groups, a reasonable expectation that every student had a working MacBook or iPad, a culture where both staff & students were used to working online in the classroom - so ditching text & exercise books was no big deal, an enormous campus, teams of ancillary staff happy to set up outdoor classrooms at a moment's notice, warm climate, & an affluent student body with no parental childcare issues, so happy to keep symptomatic kids home.
We lasted until early December & have been online ever since. Finding out in a few days if we will be back on site after half term (unlikely).
You can significantly reduce the risks, sure, but viruses gonna virus. We were smugly telling each other we had it sorted back in November.