RNA - His medical team issued a statement on Monday, confirming his transfer abroad in order to avoid further complications in his health.
"Ayatollah Sheikh Isa Qassim left Bahrain for England Monday morning, July 9, 2018.This measure has been taken on the basis of medical reports and consensus of his doctors who emphasized the need for his immediate transfer to a specialized hospital to prevent a further deterioration," the statement said.
The cleric, under house arrest since May 2017, was earlier taken to Bahrain International Airport by ambulance, local reports say.
Bahrain Foreign Minister Khalid Al Khalifah wrote on Twitter on July 6 that King Hamad bin Isa Al Khalifa had allowed Sheikh Isa Qassim to travel to the United Kingdom for medical care.
The online newspaper Rai al-Youm had quoted informed medical sources in London as saying that the top cleric is suffering from cancer, adding that the disease is in an early stage.
Sheikh Qassim was taken to a private hospital in critical condition late last year, and underwent surgery in February.
The news comes as the Al Khalifah regime seeks to silence the opposition and put its leaders in jail, send them into exile or revoke their citizenship.
On May 21 last year, a Bahraini court convicted Sheikh Qassim of illegal collection of funds and money laundering, and sentenced him to one year in jail suspended for three years. It also ordered him to pay $265,266 in fines in a ruling which sparked widespread demonstrations across the kingdom.
According to Press TV, Bahraini authorities stripped the cleric of his citizenship on June 20, 2016. They later dissolved the Islamic Enlightenment Institution founded by Sheikh Qassim as well as the opposition al-Risala Islamic Association.
Anti-regime protesters have held demonstrations in Bahrain regularly since February 2011.
They are demanding that the Al Khalifah dynasty relinquish power and allow a just system representing all Bahrainis to be established.
Manama has gone to great lengths to clamp down on any sign of dissent. On March 14, 2011, troops from Saudi Arabia and the United Arab Emirates were deployed to assist Bahrain in its crackdown.
Scores of people have lost their lives and hundreds of others sustained injuries or got arrested as a result of the crackdown.