Thames Water engineers have unearthed a half kilometre wall of congealed fat lurking beneath the roads outside Heathrow Terminal 5, a blockage big enough to stretch between two airport terminals.

The fatberg, which filled around 500 metres of the 1,030-metre sewer, was discovered beneath Poyle Road, an area dominated by industrial units and airport perimeter businesses. As this section of sewer stays full for long periods, fat deposits build up quickly, affecting multiple manholes and causing repeated blockages.

Removing the Heathrow fatberg took over two weeks, from 16 February to 10 March, with teams still working on a dig to repair a collapsed section of the sewer. Engineers used excavation tools to chip away at the solid mass before blasting the remaining deposits with high-pressure water jets.

Steve Crabb, Head of Waste Operations for Thames Water home counties, said:

"This was a stubborn and sizeable blockage, but our teams have worked relentlessly to break it down and keep the network flowing. Fatbergs like this are entirely avoidable, and we're urging everyone including businesses to think carefully about what they pour down the drain to help us prevent repeats of this in future."

Across the Thames Water network, fats, oils and grease cause more than 20,000 blockages every year, accounting for 28% of all sewer blockages. These blockages lead to over 60% of sewer floods and cost around £40 million annually.

Research commissioned by Thames Water shows that many residents across London and the Thames Valley are unknowingly contributing to the challenge. A recent survey found that: more than 40 per cent of people had poured meat juices down the sink, 39 per cent gravy, 18 per cent animal fats including lard, 28 per cent cream, 21 per cent custard and 10.5 per cent hummus – all fatty and oily substances that can congeal in pipes and block them up.

Thames Water said works closely with businesses to prevent grease entering the sewer system, offering guidance on proper kitcit hen waste management, the use of grease management systems, and the legal implications of discharging fats, oils and grease into drains.

To help residents and businesses "starve the fatbergs", Thames Water is sharing the following tips: