The white-boarded, slate roofed building beside the arch which now leads into the new Forge Lane houses is the original village watchman’s hut and was erected in 1787.

The watchman was probably armed with musket or pistols to guard against highwaymen and deal with vagrancy and drunkenness. In 1787, the Petersham watchman was paid 11 shillings a week to guard the village from 9pm to 8am.

After the Metropolitan Police were formed in 1829, most lock-ups became redundant but the Petersham lock-up survived because the council used it as a storeroom for tools.

In 1955, some villagers wanted it to be demolished but the Ancient Monuments Committee decided it should be preserved. It is now a Grade II listed building and due to representations by the Environment Trust, it is on the English Heritage list of important buildings at risk.