A 'fatberg' blocks a sewer
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Fatberg plague: BBC gets close-up look

25 April 2014 Last updated at 07:50 BST

Huge lumps of oil and grease caused by pouring hot fat down the drain are costing water companies around £79 million a year to tackle.

The BBC's John Maguire takes a close look at "fatbergs", which are causing problems in London's sewers.