Staff at the venue where Liz Truss was pranked while on stage say they believe they know how the political activists behind it organised the stunt.

Officials from Beccles Public Hall say the 'lettuce' banner which was unfurled over the head of the former prime minister may have been installed by someone during a previous booking.

Ms Truss was being interviewed on stage when the sign, saying "I crashed the economy" gradually descended above her.

She walked off and the event on Tuesday, to promote her book 10 Days to Save the West, was brought to a swift close.

Liz Truss continued to talk before realising there was a banner Liz Truss continued to talk before realising there was a banner (Image: Submitted)

READ MORE: Liz Truss calls lettuce stunt at Beccles Hall 'not funny'

Lee Johnson, chairman of Beccles Lido Ltd - which runs the venue - said staff had launched an investigation and that he had a "strong" theory about what had happened.

He told the BBC: "I'm not 100% sure how it happened, but we have got our strong theories around how it happened.

"We think the hall had been potentially hired by someone and that's when the device was put in place.

"I am working with Richard [Melchior, venue manager] to ensure that any future bookings are looked at more stringently, to ensure that this sort of thing does not happen again.

"It is an unfortunate event. I do want to reiterate that Beccles Public Hall was not involved in this at all; that has been brought by Led By Donkeys, but it has put Beccles Public Hall on the map."

The stunt was carried out by a group called Led By Donkeys, which was set up by anti-Brexit campaigners and has organised a number of pranks on politicians.

The lettuce was a reference to another stunt organised by the Daily Star newspaper, which set up a webcam on lettuce while Ms Truss was prime minister to see if the salad item would last longer than her stay in Number 10.

Ms Truss has said the Beccles incident was the work of "left wing activists" and was an attempt to curb free speech.

"This is done to intimidate people and suppress free speech. I won't stand for it," she said.

"Would we see the same reaction if the activists were far-right?"

A man was detained after the event (Image: Submitted)

A 50-year-old man was arrested on suspicion of burglary after the incident but was later released without charge and will face no further action.