A FIVE year, £25m maintenance programme on Cumbria's world famous Thirlmere Aqueduct finishes today.

The aqueduct has been shut down temporarily for about a month every October since 2005 to allow specialist engineering contractors to get inside safely.

Engineers opened the final valve at 9am this morning, which will permanently fill the structure with water.

This means that it will be at least 10 years before anyone plans to set foot inside the underground tunnel again.

Hewn from Lake District rock around 120 years ago, the 84 mile long aqueduct carries 220 million litres (over 58 million gallons) of drinking water from Thirlmere reservoir every day using gravity as the only source of power.

The aqueduct forms an essential part of the drinking water supply network for hundreds of thousands of people living along the length of the aqueduct between Cumbria and Manchester.

United Utilities' regional supplies and aqueducts manager John Butcher, who has overseen the project, has spent many hours inside the tunnel since 2005.

"It's quite sad to think I may never go inside it again,” said Mr Butcher, from Kendal.

“I have nothing but admiration for those Victorian engineers who built it.

"We have done some repairs to the structure, sealed some holes and stabilised some mountainside, but it was in astonishingly good condition given its age.”

Shutting down such an important source of water takes a lot of planning and Mr Butcher has painstakingly monitored every aspect of water supply and safety.

“It’s all about making sure our future water supplies are as high quality and reliable as they have always been,” he added.

"Once the water has started to flow again, there are no plans to stop it again for over a decade.

"I was there at Thirlmere to watch the flow control valve as it is opened and hear the roar of the water as the aqueduct is brought back to life.

“I didn't want to miss the successful end of such an enormous programme of work that is so essential to so many people, has been such a big part of my life and happened without supplies being affected to a single one of our customers.”