This episode is set in the fictional Langley Hall Borstal for Girls. A Borstal was a custodial institution introduced in 1902 for young offenders in the UK. The first was established at Borstal Prison in a village called Borstal, near Rochester, Kent, England.
The Criminal Justice Act 1982 abolished the Borstal system in the UK, replacing them with youth custody centres.
This is only the second episode in nine series not to feature Mrs. McCarthy (Sorcha Cusack), the first being the previous episode S9 E7, The Island of Dreams (2022).
The stop sign is incorrect. It should be the word "STOP" in a red triangle pointing down within a red circle. The octagonal sign seen here wasn't introduced until 1975.