Thames Water is sending specialist workers armed with pneumatic drills underground to demolish the biggest “concreteberg” ever found in London’s sewers.

The mass is 100 metre-long (328ft) rock-hard blockage under the streets of Islington was discovered during a routine check earlier in April.

Clogging three major sewers it will take at least two months to break up.

Furious Thames Water bosses condemned the “mindless abuse” of its network and have said it could cost up to £1 million / 1,156 milloin eur to tackle the obstacle, estimated to weigh more than 100 tons.

The previous biggest was an 80 metre-long “berg” found in Twickenham in 2017, although that was in a much smaller pipe.

The new concreteberg is believed to have been caused by a construction company pouring surplus cement down a drain