Sadowski was given the first sentence for attempting to procure a child under 16 and, unusually, a second consecutive sentence for possessing an imitation gun. In most cases a second sentence is served concurrently.

Judge Gerald Gordon, sitting at Southwark Crown Court, said that current legislation prevented him from passing a higher sentence on Luke Sadowski, 19, who was caught in a joint operation by American and British police.

Current rules also mean that Sadowski will not have to go on the sex offenders' register.

The judge said: “It is hoped that urgent consideration will be given whether that maximum gives adequate powers to the court to protect the young and vulnerable.”

The law is now being changed and anyone charged with a similar offence in a year's time could face a maximum of 14 years. But that will come too late for Sadowski who was trapped by his use of a website set up by US agents to detect paedophiles. When Sadowski — a student at Canterbury Christchurch University College — continued asking to be introduced to a young girl, they alerted Scotland Yard’s paedophile unit.

Officers taped and videoed Sadowski as he came to London to rendezvous with a fictitious nine-year-old at a hotel and he was arrested. He was carrying an imitation gun, a teddy bear and a condom. Later they found an array of weapons at his home.

Judge Gordon told Sadowski there were a number of features in the case which “give rise to real serious concern about the danger you may pose to women”.

He had read psychiatric and probation reports which also indicated “elements of fantasy and bravado”.

After the conviction NSPCC policy adviser Christine Atkinson said the change in sentencing could not come quickly enough. She said: “It’s a priority that the proposed legislation is implemented as soon as possible to protect children.”

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