LONDON (Reuters) - (Backstory is a series of reports showing how Reuters journalists work and the standards under which they operate)

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A tip-off, a red traffic light and knowledge of the dense streets around London’s Savile Row ensured father and son Reuters photographers Peter and Henry Nicholls had the first and only photographs for 20 minutes of WikiLeaks founder Julian Assange as he left a police station on his way to court.

Raising a handcuffed hand from the darkness of the police van to give a thumbs-up sign, Assange stares at the camera, his white hair, beard and pallid face making him appear far older than his 47 years.

Photographer Peter Nicholls was initially disappointed not to have been at the Ecuadorean embassy, where he had been holed up since 2012, when officers removed him.

“Having spent many times over the last seven years door-stepping the Ecuadorean embassy, to find he had been taken away was a real ‘aargh!’ moment,” he said.

“Then we got some information that he was at Savile Row police station, so we went there.”

Peter and his 29-year-old son, Henry, found themselves alone outside the station.

They recognized a police van that had been outside the embassy by its number plate. That convinced the photographers that the tip-off they had been given in advance about Savile Row was accurate.

“It was clear he was there because they were stopping us from moving any closer. There was more activity than usual,” said Peter.

About 90 minutes after the photographers got there, a convoy of three police vans arrived. One reversed into a drive-in garage behind a shutter. When it pulled out with Assange on board, Peter and Henry were waiting on each side of the drive.

“We photographed the vehicle from both sides, it had this horrible dark smoky glass,” said Peter. “We knew the route it had to take to get out of the facility toward the court so we ran around the block and caught them a second time.”

“Thankfully, the traffic lights turned red, the police convoy didn’t have its blue lights on, so they just sat there for a few seconds and gave us a chance to catch up.”

The pair snapped the figure through the window.

“We looked at our cameras and saw we had cracked it.”

Henry and Peter Nicholls often work on the same story, but rarely are they the only photographers present.

“Today we were lucky that we had no other competition, our only competition was each other.”