The crumbling farm buildings searched by Maddie cops this week have clearly had regular visitors over the years.

The four isolated plots, spread across a large area of overgrown clifftop coastline in Portugal, are covered from floor to ceiling with graffiti. Empty beer bottles and cans are scattered across the ground outside, showing they may have been popular meeting spots for the local youths.

By the entrance of one of the buildings there were even four pairs of discarded women’s knickers. Approaching the derelict buildings, the day after the police ended their search, a few signs remain to show officers were there.

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A couple of strips of tape are trailed between bushes, while a number of trees around the buildings have been chopped back. Piles of rubbles and brambles can be seen outside each building where police have cleared a path for their forensic teams to enter.

They also cleared the area around an old drainage well, which holds a pool of stagnant water at the bottom, which clearly became part of their investigation. Walking into the shells of the building - with their collapsed roofs and flaking walls - shows the police have cleaned them out. There are no brambles or bottles inside.

The floors inside were swept tidy, with the original blue and white tiles visible in one of the outbuildings. But it is obvious the vandals and graffiti artists have also seen them as easy pickings over the years. The huge amount of graffiti - including artwork of sinister faces, cartoon characters, swear words and random spray paint scribbles - shows that there have been many people paying a visit.

It is unclear when the buildings were abandoned, but those who headed into the scrublands over the years would have had no idea that, one day, it would become the scene of a major police investigation.

German police, aided by their Portuguese colleague, spent three days scoring the buildings this week, using JCB diggers and a ground penetrating radar. They were hoping to find clues in the 18 year investigation into the disappearance of three-year-old Madeleine McCann.

Little Maddie went missing from her holiday apartment on the evening of May 3, 2007. Her whereabouts remain unknown, although German prosecutors believe she is dead. Maddie had been on holiday with mum and dad, Kate and Gerry, along with her twin siblings and a group of family friends when she vanished.

This week German and Portuguese officers covered a huge swathe of coastal scrubland between Praia da Luz - where Maddie and her family were staying - and the town of Lagos. The site is close to where German investigators prime suspect Christian Bruckner had been living at the time. He denies any involvement in Maddie’s case.