"The British government has shown flawed reaction to this incident from two aspects; first it had not adopted the necessary measures to prevent it; second the government in London procrastinated ending the incident and as the incident could end much earlier, it took two hours," Araqchi said.
"The British government has extended its formal apology, voiced regret and used the word apology (in phone talks with the Iranian officials)," he said, adding that the process of trying the attackers is also underway.
Araqchi said that London police have also increased security measures and deployed forces around the Iranian embassy.
Several Britain-based Shiite extremists affiliated to Sadeq Shirazi sect attacked the Iranian embassy premises in London last Friday, while menacing the staffers with cold weapons.
Four men opened their way into the embassy premises at 16:30 local time, while threatening people on the scene with machetes and baseball bats. The London Police deployed around the embassy but took no action in the first couple of hours after the attack. Later reports said the attackers were arrested after three hours.
The slow pace of police measures against the attack enraged Tehran.
Iranian Supreme Leader's top aide for international affairs Ali Akbar Velayati lashed out at the UK government for neglecting its duties.
"The British government is definitely responsible for protecting the safety and security of political representation delegations in that country, including the Iranian embassy in London, and they have taken flawed action to stop the raid of a number of thugs who have been selected by foreigners," Velayati told reporters in Tehran on Saturday.
"Had the British government and police wanted, they would have managed to stop the raid of some thugs on the Iranian embassy," he added.
Velayati said that the British government should account for its ignorance and flawed performance.