Newly-released security camera video shows a 15-ton blob of sewage waste made of festering food fat and baby wet wipes trapped inside a London sewer.

The so-called "fatberg" (as in "iceberg" of fat) was discovered by sewer workers in the Kingston neighbourhood of south London.

The blockage, which reduced the sewer's working capacity to just five per cent, was only discovered after area residents said they could no longer flush their toilets.

It took sewer workers three weeks to clear the giant lumpy mass, said Thames Water who manages the city's sewers.

Work is now being carried out to repair the damage caused to the pipes in the English capital.