Who were the investigators and what did this little-known organisation do?

Our new temporary exhibition, ‘The Great Train Robbery: Crime and The Post’ uncovers the work of the Post Office Investigation Branch. Read on to find out all about this little-known organisation and its workers.

What is IB?

The Post Office Investigation Branch (IB) is the oldest recognised criminal investigations force in the world. For more than 335 years it has worked to detect offences against the post and prosecute the perpetrators of these crimes.

The Post Office Investigation Department Logo on a plaque © The Postal Museum

The work of the Investigation Branch

Post Office Investigators undergo intensive training for their roles, including methods for establishing dishonesty, interview techniques, preservation of evidence and preparation of cases for consideration by the prosecuting authority. The unit includes crime prevention surveyors who carry out inspections of postal premises and security operations, as well as information systems analysts who monitor patterns of crime.

The Latin motto of the Post Office Investigation Department was

‘Suaviter in Modo, Fortiter in Re’ – meaning ‘Gentle in Manner, Resolute in Deed.


Cases tackled by the Investigation Branch during its history have included everything from multimillion-pound heists, vicious murders, stamp frauds and forgeries, to dog attacks on postal workers.

Investigator’s Hard Hat designed to protect the wearer during potential attacks, c1950

As well as crimes committed by the public, the unit also investigates offences by postal staff. In some cases, this work has involved investigators going undercover to infiltrate post offices and observe the activities of postmen and postwomen.

Investigating the ‘Crime of the Century’

In the 1960s Post Office Investigators worked in collaboration with the police to solve The Great Train Robbery, in which a gang led by Bruce Reynolds stole £2.6 million from a Royal Mail train travelling from Glasgow to London.

Page one of the report by Richard Yates, Assistant Controller of IB (POST 120/95)

A Senior IB Officer was sent to the scene of the crime and all other IB officers engaged on the Mail Bag Section ‘presented themselves for duty’ at Post Office HQ on St. Martin’s Le Grand in Central London.

Reporting for duty at Post Office HQ IB Investigator Harry Lyons and a colleague, Frank Cook, were met by an ashen-faced private secretary.

“He had a long face and muttered something about ‘Everybody’s gone mad today’.”


A press conference, held jointly by the Post Office and Buckinghamshire Police in Aylesbury that afternoon, attracted more coverage around the world than any other event in the history of the Investigation Branch. The banks affected reacted quickly and organised an unprecedented award of £250,000. The Postmaster General, Reginald Bevins, added a further £10,000 to that figure.

Postmaster General Reginald Bevins © Keystone Press / Alamy Stock Photo

One of the IB’s first tasks was to investigate the rumours of an ‘inside job’ – fuelled by the fact that all three of the secure HVP coaches were simultaneously out of action for the first time, plus the gang’s apparent knowledge of the lack of security on the reserve HVP coach, the exact layout of the train, and the unusual amount of cash being carried on board that morning.

All 77 of the Post Office staff present on the train were background checked and interviewed at length by Lyons and his colleagues.

Documents room for the Great Train Robbery investigation © The National Archive

Investigators pulled together suspect lists within days of the Great Train Robbery and the first arrests were made within a week. By January 1964, enough evidence had been gathered to try 12 of the gang and 11 of them received heavy sentences of 20 to 30 years.

Three more suspects were arrested and jailed within five years of the crime, but two escaped from prison during that period, and the identities of a number of the gang have never been confirmed – including the rumoured Post Office insider.

Despite intense speculation and the enquiries led by the Investigation Branch ‘no evidence of collusion came to light’ and no proof of a Post Office insider has ever been found.

Investigation Branch today

During the late 1900s and early 2000s the organisation of the postal prosecution and investigation services has changed alongside the various businesses responsible for carrying and delivering mail in the UK.

The IB became the Post Office Investigation Department (POID) in 1967 and later changed its name again in 1996 to Post Office Security and Investigation Services (POSIS).

Today, both Royal Mail Group and Post Office Ltd have operational Security and Investigation teams, led by Head of Security and staffed by professional investigators and security managers. The Post Office Solicitors’ Office has been succeeded by Royal Mail Legal Services, which continues to be recognised by the Ministry of Justice as a private prosecutor in England and Wales.

View original records and artefacts in our new exhibition that reveals the untold story of the ‘Crime of the Century’ – through the personal accounts of the victims and the detectives who worked tirelessly to bring the offenders to justice.

– The Postal Museum Team