More than 10,000 followers of the Ahmadi movement thronged the grounds of the Bait-ul-Futuh "mosque" in London on Friday to celebrate the opening of the building.
The Ahmadis consider themselves Muslims but are rejected as such by mainstream Muslims.
Hadhrat Mirza Masroor Ahmad, the fifth "worldwide supreme head" of the Ahmadi community, led inaugural prayers at the "mosque", which features two towering minarets, a library, three conference rooms, a gym and a dome 23m high.
It will be able to house 10,000 people, with 4000 fitting inside two segregated prayer halls.
During the ceremony, the British flag was raised above the building and 76 doves, representing each of the Ahmadi centres in Britain, were released into the sky.
"We built the very first London mosque in 1924," claimed Rafiq Ahmad Hayat, head of Britain's Ahmadi community, before the ceremony.
"This time we have produced the largest and most sophisticated mosque in Britain to serve as a landmark for the next century."
The Ahmadi centre cost $16.4 m
The $16.4 million cost of the building was raised entirely from individual donations, mainly from British worshippers but also from abroad, according to Basharat Nazir, spokesman for the Ahmadi community in Britain.
"We are the renaissance of Islam. We stand for moderation," he said of the Ahmadi's belief that Islam cannot be imposed by force and non-belief in jihad.
The Ahmadi movement was founded in the Indian town of Qadian in 1889 by Hadhrat Mirza Ghulam Ahmad, who claimed to be a reincarnation of the Prophet Muhammad as well as an incarnation of the Hindu lord Krishna.
Ahmadis claim they have more than 200 million followers in 174 countries, although these figures are often disputed as a wild exaggeration.
The Muslim Association of Britian said on Friday the so-called mosque should be really be called a "prayer space".
" The Ahmadi community are regarded as non-Muslims by all Muslim scholars and groups worldwide because of the Ahmadi's central belief that Mirza Ghulam Ahmed was a prophet and the promised Messiah"
Muslim Association of Britain
In a statement it said: "The Ahmadi community are regarded as non-Muslims by all Muslim scholars and groups worldwide because of the Ahmadi's central belief that Mirza Ghulam Ahmed was a prophet and the promised Messiah.
"Mainstream Islamic teaching holds that the blessed Prophet Muhammad (peace be upon him) was the last in a long line of Prophets sent to mankind. Mainstream Sunni and Shia Muslims are both agreed on this basic tenet of the Islamic faith."
The association added: "We believe that there are no more than one million Ahmadis in the entire world as opposed to the 1.5 billion strong worldwide Muslim community.
"So, whilst we fully accept the right of Ahmadis to their own religion, it is clearly misleading to describe them as Muslims. They are not."