The London Siege was first put into effect when British Prime Minister James Wilson was mysteriously killed. The Barkawi Arms Network would to assassinate several leaders of Western nations in retaliation of the death of Barkawi's family members. Many of them disguised themselves as the Metropolitan Police, Queen's Guard, and first responders to coordinate the attacks. MI5 Center Intelligence Chief John Lancaster also joined the terror plot as a mole as he believed that decreasing military budgets is making the United Kingdom vulnerable to terrorism.
After Benjamin Asher and several other world leaders arrived in London to attend the funeral, one officer secretly attached a bomb to the limo of Canadian Prime Minister Robert Bowman. A few seconds later, the limo exploded, killing Bowman and his wife.
After, several Islamic terrorrists disguised as the Metropolitan Police killed the other police officers before more terrorists in the crowd joined in on the attack. Though Mike and Bronson took out some of the terrorists, the U.S and British security details were decimated.
While Italian Prime Minister Antonio Gusto and his wife were watching the scene from Westminster Abbey in shock, a bomb detonated on one of the towers, killing them. Several more civilians were killed by the falling rubble.
Unable to seek refuge with Leighton Clarkson or use The Beast, Mike requested a Land Rover to take them back to London Stansted Airport so they could escape via Air Force One. While attempting to draw the terrorists off, Bronson was killed before he could escape with Ben, Lynne and Voight. The four were pursued through the streets of London by more terrorists. In the ensuing chase, all the terrorists chasing them were killed, though Voight was fatally shot. Once they boarded Marine One to get to the airport, they faced the threat of stinger missiles. Marine Two and Marine Three were taken out, leaving Marine One defenseless. As Marine One was about to be shot down, Mike told everyone to brace for impact, leaving the three for horrified for what was about to happen. Marine One crashed in Hyde Park. Though Ben and Mike survived, Lynne was fatally injured and died of her wounds, but not before telling Mike to stay alive and to make the terrorists pay as Mike tearfully watched his boss die. As more terrorists on motocyles converged on the crash site, Mike and Ben fled out of Hyde Park.
Later, after killing a terrorist to obtain weaponry, Mike and Ben fled to the London Underground where they where ambushed by terrorists led by Raza Mansoor. However, Mike killed them all and interrogated Raza. After Mike answered a call over a radio from Kamran Barkawi, Kamran threatened to execute Ben on live media should he and his men capture him. However, Mike was unfazed and killed Raza over the radio to show them he meant business, much to the horror of Kamran and Raza's brother, Sultan Mansoor, who lost his legs in the drone strike.
As evening came, Ben and Mike traveled to an MI6 safe house, where they met MI6 agent Jacqueline Marshall and her colleague Pradhan. Taking refuge there, Jax revealed that the mastermind behind the attacks was Aamir Barkawi, to which Ben revealed that Barkawi was an arms dealer shielded by corrupt governments and that the attacks were motivated after a failed attempt by the G8 leaders to kill him Pakistan, which claimed the life of the daughter, Amal. Later, after Ben and Mike engaged in a conversation, a Delta Force team was dispatched by Allan Trumbull to escort the two the U.S Embassy. However, Mike soon realized that the team were actually disguised terrorists and intercepted Trumbull's message. As a result, Ben was secured in a room as Mike went to the armory. Jax, who suspected a mole in the British government, went to Box Command to restore the CCTV systems and expose the traitor. After Mike took out the terrorists, the two fled for the U.S Embassy as numerous terrorists attempted to thwart their escape with gunshots and landmines. Just as things were beginning to look good, a truck rammed the vehicle, causing it to flip. As a result, Ben was captured and taken to the terrorist hideout for the live execution. Meanwhile, Mike encountered a joint squad of Delta Force and Special Air Service commandos led by Will Davies. Together, they attacked the terrorist hideout while Mike stopped the live execution. In the aftermath, a gas explosion destroyed the hideout, killing Kamran and the remaining terrorists while Mike and Ben took shelter in an elevator shaft. With Ben rescued, Mike gave Karman's phone to Will in hopes that he could track down Barkawi with it.
Meanwhile, Jax found Lancaster as he was trying to flee the country, who was the mole. Jax confronted him on his actions before demanding him to surrender. When Lancaster refused to turn himself in as his treason would most likely result in execution, Jax shot Lancaster dead after he tried to go for the gun in his truck.
Later, Barkawi received a call. Though he assumed it was Kamran, it was Trumbull who called. Shocked and angered, he warned the Vice President that his war wasn't over. When Trumbull advised Barkawi to look out his window, Barkawi looked up and gives a defeated smile. Seconds later, another drone strike hits the compound, putting an end to Barkawi for good and avenging the fallen world leaders and all those who perished in the London Siege.
The London Siege was impacting, especially to Western countries. Parts of London were decimated and five G7 leaders were assassinated with only Leighton Clarkson and Benjamin Asher surviving. Many civilians, Metropolitan Police officers, and Secret Service agents were also killed. However, President Asher's assassination was thwarted in time, thanks to Mike Banning and a joint SAS/Delta Force team led by Davies.
Two weeks after the attacks and subsequent death of Aamir Barkawi by another drone strike, London began to rebuild and Clarkson's reign as Prime Minster began with a new government installed. Leah had also given birth to their new daughter whom Mike named after his late boss to honor her. After hearing a speech from Vice President Trumbull on TV, Mike decided to delete his resignation letter and continue serving in the Presidential Detail.