Congealed lard is seen stuck to the roof of a London sewer.

AFP/London

A 15-tonne ball of congealed fat — dubbed Britain’s biggest ever “fatberg” — has been dredged up from a London sewer, utility company Thames Water said yesterday.

It took 10 days to remove the double-decker bus-sized lump of festering food fat mixed with sanitary wipes which formed in drains under a major road in Kingston, southwest London.

Local residents in the well-to-do suburb complained that their toilets would not flush.

Had the colossal “fatberg” not been removed, it could have led to raw sewage flooding homes, streets and businesses, Thames Water said.

“While we’ve removed greater volumes of fat from under central London in the past, we’ve never seen a single, congealed lump of lard this big clogging our sewers before,” Gordon Hailwood, waste contracts supervisor for the company, said in a statement.

“Given we’ve got the biggest sewers and this is the biggest ‘fatberg’ we’ve encountered, we reckon it has to be the biggest such berg in British history.

“The sewer was almost completely clogged with over 15 tonnes of fat. If we hadn’t discovered it in time, raw sewage could have started spurting out of manholes across the whole of Kingston.

“It was so big it damaged the sewer and repairs will take up to six weeks.”

Images from inside the sewer showed that the rotting mound of fat had reduced the 70 by 48-centimetre (27-inch by 19-inch) drain to five percent of its normal capacity.

While the risk of stomach-churning sewage belching up through people’s toilets might have been averted, Londoners could soon be washing with it anyway.

CountyClean Environmental Services, the waste management company that removed the deposit, said it would go to good use.

“We recycle everything that we remove — the water is extracted and the remaining fats and oils are turned into products like soap, biodiesel and fuel,” a CountyClean spokesman said