PC Mick Wass, his rider during his time at the Met, said, "Chiswick has always liked to think he is the one in charge, but he has always looked after me."
Jeanette Allen, Chief Executive of The Horse Trust, said: "Chiswick is a real hero and it is a privilege to be able to provide him with a dignified retirement after spending a lifetime bravely serving the people of London."
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The Hammers moved to the Olympic Stadium in May leaving their old site to be developed for housing.
The first officer shouted "look!" as the drone passed next to the right wing at around 11,000ft above south-east London.
They found a sheepish looking ewe with a traffic cone on her head in the middle of a field.