They now face a ‘roadblock’ as no useful clues were found in the three-day joint operation between German and Portuguese police earlier this month.

That’s despite soil from the Barragem do Arade reservoir, around 30 miles from where Madeleine was last seen in May 2007, being taken to Germany for testing.

A source close to the investigation told The Sun: “Sadly, it’s looking increasingly like the search of the reservoir will not provide any answers or fresh leads.

Read more: Madeleine McCann police seize ‘a number of items’ after reservoir search in Portugal

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“Despite using some of the most high-tech forensic kit available none of the items have proved to be of use. 

“It feels like a bit of a roadblock has been hit.”

Prime suspect Christian Brueckner once called the area his “little paradise”.

Eight holes around 2ft deep were also drilled, suggesting officers were looking for buried items or soil samples.

Brueckner is currently behind bars for the rape of a woman close to where Madeleine McCann disappeared.

He’s also suspected of further rapes and child sexual abuse committed in the area between 2000 and 2017.

He has reportedly denied any involvement in Madeleine’s disappearance.

Madeleine was three when she vanished while on holiday with her parents in Praia da Luz, after they left her and her younger twin siblings asleep in their apartment while they went out to dinner with friends.

Portuguese lawyer Marcos Aragao Correia previously claimed that criminal contacts had told him that Madeleine’s body was in the reservoir.

In 2008 he raised funds for unsuccessful private searches of the water.

The latest searches came as the Home Office granted an extra £110,000 in funding this financial year for the Metropolitan Police to assist with finding Madeleine, down from just over £300,000 last year.

The total funding given to Operation Grange has been just under £13.1 million since 2011.