Four men have been cleared of raping a woman at a college ball at the Royal Agricultural University after their trial collapsed on the day it had been due to open. Prosecutors at Gloucester crown court offered no evidence against Thady Duff, 22, James Martin, 20, Leo Mahon, 22, and Patrick Foster, 22. Duff, Mahon and Foster were students at the college in Cirencester, Gloucestershire, while Martin, an apprentice farrier and amateur jockey, was visiting them.

All four were accused of raping the woman at an end of year ball in May 2014. Their trial was due to begin two weeks ago but was delayed by issues surrounding the late disclosure of evidence to the defence by the prosecution

Fiona Elder, prosecuting, told the court on Monday that after a review of the case it had been decided not to offer any evidence against the four defendants.

“The decision was made that there was no longer a reasonable prospect of conviction and therefore in the circumstances it was not for the crown to pursue this case to trial,” Elder said.

“The police were informed and discussed the decision with the head of the south-west rape and serious sexual offences unit. The head of the unit consulted with the complainant and her family to ensure they knew and understood the decision, whatever their view of it.”

Lawyers for the men expressed concern that the charges had hung over them for so long.

In court, Edward Henry, for Martin, described the case as “one long exercise in confirmation bias” and accused officers of “airbrushing” and “cherry-picking” evidence.

“We need to know the answers to some questions,” Henry added. “Why … should this have gone on for so long as it has?”

A jury of six men and six women was sworn in on 29 March to hear the case but was discharged a week later without hearing any evidence.

Judge Jamie Tabor QC had told jurors they should prepare for footage of the alleged sexual activity to be shown during the trial. “This case concerns sexual activity on a ball night at the Royal Agricultural University,” he said.

“Some of that was filmed. [There] is going to be what we call adult pornographic material – very short in length – to be watched.”

Elder told Tabor on Monday that she had been instructed to apply for a restraining order against the four defendants to prevent harassment but offered no evidence to support the application. The judge refused it and issued a warning about commenting on the case on social media.

Eleanor Laws QC, representing Duff, Jane Bickerstaff QC, for Mahon, and Kieran Vaughan QC, representing Foster, said they would be seeking to recover their clients’ legal costs following the collapse of the trial.

Bickerstaff told the court: “We are very grateful that no evidence has been offered. We have had no information as to why that decision was reached or why it took 13 months to decide to charge.”

Vaughan questioned the decision of the police not to disclose certain pieces of evidence to the defence, including text messages from the time of the allegations. A hearing will be held at a later date to consider defence legal costs.

Duff, of Swindon in Wiltshire, denied three charges of rape. He also denied a charge of sexual assault against the same woman, which is alleged to have been carried out between 1 and 31 October 2013.

Martin, of Chipping Norton, Oxfordshire, denied a single charge of rape. Mahon, of Cirencester in Gloucestershire, denied three charges of rape and two charges of assault by penetration.

Foster, of Colchester in Essex, denied one charge of rape and two charges of assault by penetration.

The internationally renowned university was, until 2013, known as the Royal Agricultural College. Founded in 1845, it was the first agricultural college in the English-speaking world.