But when an animal cruelty inspector finally tracked down the driver, he was relieved to learn the horse was in fact made of plastic.
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Shocked drivers called the RSPCA's cruelty hotline to say they had spotted the horse with its legs tied to the corners of a flat-bed trailer and its body partially strapped down during a 100-mile journey from Birmingham to Cambridge, the Cambridge Evening News reported .
The charity leaped into action but when inspector Richard Lythgoe tracked down the trailer in question he laughed out loud - because the horse was made of plastic.
The RSPCA's Richard Lythgoe after tracking down the horse
He said: "When I got to the house to look into it all I realised it was a life-size plastic horse."
The couple who own the plastic animal had driven from Cambridge to Birmingham to collect it, but had to bring it back tied to the trailer because it was so big.
Mr Lythgoe said: Obviously when driving down the motorway and catching a glimpse of this life-size, life-like horse being pulled down the motorway, it would have been very worrying so thankfully it was just a fake one.
"We do get lots of calls about horses through to our hotline - but I have never been called out to check on a fake one before."