Ajmal Masroor, who regularly comments on British-Muslim issues, worked at the Fitzrovia Mosque, also known as Goodge Street mosque in central London, which is run by the Saudi-funded Muslim World League.
The imam led Friday prayers once a month at the Muslim World League's offices and ran marriage counselling sessions there before they were cancelled by the mosque.
Masroor's firing took place just days after he used his personal Facebook page to post a Middle East Eye video and describe the Saudi royal family as being "corrupt, despotic and totally anti-Islamic".
In another post, the imam had also criticized Saudi Crown Prince Mohammed bin Salman and his campaign to arrest activists and Islamic scholars.
"I am 100 per cent sure that they fired me because of my comments about Mohammed bin Salman where I said he was not a reformer but a conformer," said Masroor.
"When I asked why they were firing me, I was told that it was an order that had come from the top. Which means the Saudi government wanted me out."
He said the mosque management had previously reprimanded him for his vocal criticism of the Saudi royal family, stating that he was permitted to criticize Saudi Arabia online, but not inside Goodge Street mosque.
"In the last five years, I was reprimanded at least five times by the management for my comments about Saudi Arabia," Masroor said.
"They would ask me not to speak about the king or the Saudi regime. I had several heated arguments with the current director on this issue.
"In the end, we agreed that I would not criticize Saudi Arabia in my sermons, but [I was] allowed to post my views online, which I regularly do."
Masroor, who leads Friday prayers at mosques across Britain, also works as a charity fundraiser, had previously run for political office for the Liberal Democrats in 2010 and was the chairman of the Islamic Society of Britain.
In a statement released online, the Muslim World League said it had "no option" but to fire Masroor from his position at the mosque.
"It was agreed with him that the mosque pulpit is not the place to attack people, governments, group or sector to express certain political views," said the Regional Director of the Muslim World League.
"He (Ajmal Masroor) continued provoking public opinion against the individuals, governments, causing a stir in the society, shaming and accusing falsely, no option was left but to stop dealing with him in any way."
The League also distanced itself from claims made by Masroor that the mosque had only given space to Saudi projects.
Founded in 1962, the Muslim World League is one of many Saudi funded groups established to spread its Wahhabi doctrine. Using the Goodge Street mosque as a base in London, the league ran classes and held regular services for the local Muslim community.
According to the Pew Research Center, the Saudi government had given approximately $13m in 1980 to the Muslim World League. This figure has said to have grown since.
The research center also notes that the Muslim World League's primary goal is to give "Muslim Youth access to the strict interpretation of Islam advocated by the Saudi religious establishment."
Source: Middle East Eye