Walid Saadaoui, 38, and Amar Hussein, 52, were both convicted on Friday after a trial at Preston Crown Court, which began a week after an unrelated deadly attack on a synagogue in the city of Manchester, in northwest England.
Prosecutors said the pair were Islamist extremists who wanted to use automatic firearms to kill as many Jews as they could in an attack in Manchester.
They were found guilty little more than a week after a mass shooting at a Jewish Hanukkah celebration on Bondi Beach in which 15 people were killed.
Prosecutor Harpreet Sandhu said on Friday that, had Saadaoui and Hussein carried out their plan, it "could have been very much more serious" than the attacks in Australia and Manchester.
Judge Mark Wall sentenced Saadaoui to a minimum term of 37 years and Hussein to a minimum term of 26 years, saying: "You were very close to being ready to carry out this plan."
Hussein refused to attend his sentencing, having refused to attend most of his trial, which Wall said reflected Hussein's cowardice, describing him as "brave enough to plan to threaten an unarmed group with an AK-47 but not sufficiently courageous to face up to what he did".
Saadaoui had arranged for two assault rifles, an automatic pistol and almost 200 rounds of ammunition to be smuggled into Britain through the port of Dover when he was arrested in May 2024, Sandhu told jurors at the trial.
He added that Saadaoui planned to obtain two more rifles and another pistol, and to collect at least 900 rounds of ammunition.
"This would likely have been one of the deadliest terrorist attacks ever carried out on British soil," Wall said.
Unbeknown to Saadaoui, however, a man known as "Farouk", from whom he was trying to get the weapons, was an undercover operative who helped foil the plot.
Walid Saadaoui's brother Bilel Saadaoui, 37, was found guilty of failing to disclose information about acts of terrorism. He was sentenced to six years in jail.
