Lawrences Auctioneers of Crewkerne is offering the box, which still contains its original telephone, in its May 12 Collectors auction.
It is thought to date from between the world wars when police phone boxes were common.
There were initially two types of police boxes: a smaller version known as a police post containing just a telephone and a first aid kit while the larger version was the conventional police box that callers or police could enter. The television series Doctor Who immortalised a 1960s version of the larger type as the TARDIS time machine.
Police boxes were used by patrolling officers, before two-way radios and mobile phones were in common use, to communicate with their stations but members of the public could also use the phone to contact a police station in an emergency.
Lawrences’ Auctioneer Simon Jones, said: “This is a rare piece of telephone history and would make a great acquisition for a collector or museum. We believe there are only two left in existence in London, so this is a most unusual find.”
Made in cast iron, it was purchased by the vendor around 20 years ago, and carries an estimate of £2000-3000.