More and more young people on remand will be held in Wandsworth Prison alongside hardened career criminals, while they await trial or sentence.

The overflow of 18 to 20-year-olds into adult prisons such as Wandsworth was previously an ad hoc arrangement, made as a last resort.

But as Feltham young offenders' institution fills up with youths from the south-east, under new efforts to avoid locking them up far from home, the overspill will from this week be systematically channelled towards Wandsworth, Brixton and Wormwood Scrubs prisons.

Anita Dockley of the Howard League for Penal Reform said: "These 18 to 20-year-olds are a distinct group with a distinct set of needs and they are quite vulnerable.

But a prison service spokesperson said: "The law treats anyone over the age of 17 who is remanded to custody as an adult.

"However, all prisoners are assessed for vulnerability and risk to themselves or others."