Two men who swore allegiance to Islamic State have been found guilty of plotting to “kill as many Jewish people as they could”, in what detectives believe would have been the UK’s worst terror attack if it had not been thwarted.

Walid Saadaoui, 38, and Amar Hussein, 52, were found guilty at Preston crown court on Tuesday of preparing acts of terrorism between 13 December 2023 and 9 May 2024.

Jurors were told they were Islamist extremists with a “visceral dislike” of Jewish people. They planned a marauding attack in Greater Manchester, at the heart of one of Europe’s largest Jewish communities, having answered an Islamic State “call to arms” issued after the outbreak of war in Gaza.

Saadaoui arranged for the purchase and delivery of semi-automatic rifles, conducted reconnaissance and identified targets, but the man supplying them with the weapons was an undercover operative.

The operative, known to them as Farouk, had infiltrated jihadist social media networks and convinced Saadaoui that he was a fellow extremist.

Saadaoui, a former Italian restaurant owner, was arrested in a police sting as he attempted to take possession of two assault rifles, a semi-automatic pistol and almost 200 rounds of ammunition at the car park of the Last Drop hotel in Bolton on 8 May 2024.

The weapons were of the type used in Paris on 13 November 2015, when 130 people were killed and hundreds injured in a series of terrorist attacks.

A third defendant, Walid’s brother Bilel Saadaoui, 36, who worked in a discount shop, was found guilty of failing to disclose information about acts of terrorism on the same dates.

Walid Saadaoui, of Abram, Wigan, Bilel Saadaoui, of Hindley, Wigan, and Hussein, of no fixed abode, denied the allegations in a trial lasting almost three months.

The Saadaoui brothers, who are originally from Tunisia and had been living in the UK for several years legally, swore allegiance to Islamic State before coming to the country. Hussein, who had also sworn allegiance to Islamic State and is understood to have been living in the UK legally, had served in Saddam Hussein’s army.

Walid Saadaoui had spoken of his connections to Islamic State to “Farouk”, telling him: “I am liaising with brothers who are insiders and are operatives, and God is my witness, they are not just brothers on Facebook, they worked with me three days and we got know each other well and they had to speak to three other people to verify me, they asked me questions about creed for three days and I spoke to them on the phone.

“They explain to me the best method of conducting the operations. If we carry out the operation in winter I will be a failure, it is better to carry out the operation in the summer … in the winter everybody is at home.”

After the verdicts, the chief constable of Greater Manchester police, Stephen Watson, thanked officers and prosecutors for having “meticulously delivered upon an operation of almost unprecedented complexity”.

“It was clear throughout this trial that the scale of the offender’s hatred towards our Jewish community knew no bounds,” he said. “All too recently in Sydney, and of course here in Manchester in October – the very week before this trial began – we have felt the devastation of terrorism directed toward our Jewish community. A terrorist attack upon our Jewish friends and neighbours is an attack on us all and is an affront to all decent people in our country.”

The force’s assistant chief constable, Robert Potts, said the attack “could have been the deadliest terrorist attack in UK history” and that it had been necessary for the investigation to continue to the point where officers were satisfied they had enough evidence to get the most serious charges authorised.

“There was very real risk and danger for Farouk, who undoubtedly saved lives,” he said. “I cannot overemphasise his courage, bravery and professionalism in the role that he played.”

The head of the Crown Prosecution Service’s special crime and counter-terrorism division, Frank Ferguson, said: “The investigation and prosecution deployed a highly trained witness who made sure their plot did not succeed and secured valuable evidence directly from the mouths of the terrorists.

“They laid bare their intention to destroy lives, their long-held attitudes and beliefs as well as their credentials” in terms of Islamic State.