From the Wikipedia page 
The catacombs of London are a series of subterranean spaces in London, United Kingdom. The city's high water table limits subterranean construction.
There has been a long tradition of burial under the floors of churches, and during the period of new church construction in the Victorian era many were provided with vaults or crypts under the main structure.
There are several purpose-built crypts/catacombs, including those of the West Norwood Cemetery, which has a remarkable collection of historic monuments on a landscaped hill. The catacombs, opened in 1837, were built below chapels and included a group of 95 vaults with private and shared loculi with a capacity of 3500 coffins. Another large underground catacomb was built at Kensal Green Cemetery and a smaller one at Nunhead Cemetery. Several other cemeteries were given above ground burial structures which they described as catacombs, including Brompton Cemetery and Highgate Cemetery.
The Camden catacombs are an extensive range of passages largely underneath what later became the Camden markets, constructed in the 19th century, which were originally used as stables for horses and pit ponies working on the railways. The catacombs also included an underground pool for canal boats.