The 5-foot-long reptile was let out Saturday afternoon so it could get some exercise, London's Daily Mirror reported Sunday.
While the lizard's species was not reported, police said it was not believed to be dangerous and its owner was worried about its safety, the Mirror reported.
"It has black and white scales and short legs and is described as being a bit puffy around the neck. If seen by a member of the public, they are requested to call the police on 101 immediately so arrangements may be made for its recovery," a police force spokesman said
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