The escape of a large silverback gorilla from its enclosure at London Zoo "could have ended very differently" and must be subject to an urgent inquiry, a leading wildlife group has said.

The Born Free Foundation said the incident was a "startling reminder" of the risks of keeping dangerous wild animals in captivity.

Visitors to the popular attraction described fearing for their safety as they were ordered to take cover in buildings when the 29st dominant male ape, who had been put on a diet, got out of its den on Thursday evening.