Mark Stevens has spent years rescuing stranded whales, dolphins and other large marine mammals around the British Isles, but one event two decades ago remains etched in his mind.
"We'd never heard of PTSD (post-traumatic stress disorder) before, but down the line we realised that that's what it left us with," he recalls.
On Friday 19 January 2006, a photo appeared of a huge whale swimming in the River Thames past the Houses of Parliament.
Stevens says those at the charity British Divers Marine Life Rescue (BDMLR) had heard a whale was in the river earlier in the week but that the photo confirmed it was a northern bottlenose, a deep-diving species usually found in the North Atlantic.
A science teacher by trade, he was at work that day when he got the call to head to central London.
