AS shoppers and football fans go about their business at Middlebrook Retail Park and the Reebok Stadium they have little idea what is happening beneath their feet.

For 10ft under the ground, a team of engineers from United Utilities is working on a complex project to strengthen an historic water pipe built in the late 1800s.

The Thirlmere Aqueduct — one of the UK’s longest underground tunnels — transports water from the Lake District to Manchester and has been drained so that engineers can inspect the structure.

Built in 1894, the Victorian structure stretches from Thirlmere Reservoir in Cumbria to Lostock water treatment works in Bolton.

The shutdown is part of an ongoing £23 million maintenance programme for the tunnel and will see it taken out of use for the whole of this month to allow engineers to walk parts of its length.

Directly below Bolton’s football academy training pitches at Middlebrook, engineers are strengthening the aqueduct floor by pumping in thousands of litres of concrete.

Part of one pitch has been dug up to allow workers access to the tunnel. The grass will be replaced when the work is completed.

Residents of Crescent Road, Horwich, were originally warned that an access point may need to be opened up in the middle of the road, involving a road closure.

This would have meant deliveries for the Greenhalgh Bakery being diverted through other neighbouring streets and possible disruption for residents.

However, engineers came up with a plan to pump concrete over a longer distance so they could reach the repair section from locations further away, causing less disruption.

John Butcher, of United Utilities, said: “The aqueduct has been a crucial part of the North West’s water network for more than a century.

“That it is still in such good condition is testament to the ingenuity of our Victorian ancestors.

“Since 2006, we have been carrying out an annual shutdown to allow inspection and maintenance work to take place, ensuring the aqueduct is good for another 100 years.

“Even after all this time, it is still a thrill to walk the tunnels and marvel at the skill of those early engineers.”