On Friday, British Transport Police launched a high-profile crackdown with Cambridgeshire police and the train operating companies to combat fare-dodgers, drugs, knife crime and anti-social behaviour.

It was the first blitz of its type to be run at the city's station, and the first time two portable knife arches had been set up in the concourse to check passengers as they left their trains.

Officer in charge at Peterborough station Sergeant Paul McGregor said the operation had led to four arrests, with three people being cautioned for carrying small amounts of drugs, and one dealt with for being drunk and disorderly.

A "substantial" number of passengers were found to have travelled without tickets and were made to cough up on arriving, he added.

No knives were discovered, however, which Sgt McGregor admitted was a "surprise".

He said: "It was the first time we have used knife arches in Peterborough. Some of the police actions that we had in place were down to the fact that we are aware that on Friday evenings, there's a large amount of people that use the railway to come into Peterborough to socialise.

"The problem with knife crime is really in London, but we want to deter people here."

About 160 people were checked by the knife arches as they left the platform during the six-hour operation.

Two sniffer dogs were also used to screen passengers for drugs.

Sgt McGregor said the operation had met with a favourable reaction from many travellers, 12 million of whom passed through the station last year.

He said: "We will be using the knife arches again in the not-too-distant future.

"People need to know that possession of a knife won't lead to an early disposal, like a caution or a penalty charge notice, but to a charge and a court appearance."