Apparently (wiki) corporal punishment was legal in schools until rather shockingly late. 1986 for English and Welsh state schools, 1998 for private schools, 2000 in all Scottish schools and 2003 in Northern Ireland schools.
The wiki article refers to an incident where someone was slippered in a private school in 1993 and the teacher won the court case alleging that they had used degrading punishment. But this was a private school, not a state school.
Apparently before 1986, it was up to the headteacher whether to allow corporal punishment in state schools. Was it still actually being practiced in state schools at that point? When was the last time it was?