Constantine Metcalfe, 16 months, was snatched from his parents' home in St John's Wood on Wednesday night, said Scotland Yard.
His mother, Rania Georgopolous, 25, received three telephone calls yesterday from the man who had taken her child.
The baby was rescued when police stopped a van near Harrow Road in north-west London. He was unhurt and later reunited with his parents. A man was last night being questioned by police.
Det Supt Bill Scholes said that no ransom had been demanded by the man who telephoned the family. The boy's mother did not realise that he had disappeared until after the first two calls.
The first time that the man telephoned, at 6am, he asked 'have you told the police?' and Ms Georgopolous thought that it was a wrong number. It was not until after the second call an hour later that she checked Constantine's bedroom and found that he was missing.
The boy is the grandson of Constantine Georgopolous, described by Mr Scholes as a Greek shipping magnate.Reuse content