It added that not a single external window grille was replaced, despite the escape of two prisoners in 2016.

They screamed for help from behind window grilles at 5.40am.

In the test several of the devices were mounted on to window grilles in a grid formation.

The kitchen underwent a renovation in the late 1950s, while a metal front door and metal window grilles were installed at a later date.

Window grilles overlooking the estero have vertical floral stems with flowers sized to small squares, while grilles facing the street display abstract interpretation of lyres.