The Bait’ul Futuh Mosque is the largest mosque in Western Europe and fifteenth largest in the world with an area of 5.2 acres (21,000 m2),

Baitul Futuh

the mosque complex can accommodate up to 10,000 worshippers. Built in 2003 at a cost of approximately £5.5 million, entirely from donations of the Ahmadiyya Muslim Community, it is located in the south-west London suburb of Morden, next to Morden South railway station, 150 yards from the Morden Underground.

source : http://thewondrous.com