Child safety campaigners have accused the Government of "dragging its feet" over a law giving police new powers to tackle paedophiles.
An offence created to target those who groom young victims online has yet to be formally triggered in England and Wales- nearly two years after it was placed on the statute book, according to the NSPCC.
Under Section 67 of the Serious Crime Act 2015 a person aged 18 or over commits a crime if they send a sexual communication to a child aged under 16 for the purpose of sexual gratification.
The Act received Royal Assent in March 2015 but the NSPCC said the Government has not yet brought the new offence into force as regulations need to be laid before Parliament before it can be commenced.
A similar law is already in place in Scotland, where authorities have recorded more than 1,500 offences, while legislation has also been in place in Northern Ireland since February last year, according to the charity.
The Government announced plans to create the new offence in 2014 after a campaign from the NSPCC.
Its chief executive Peter Wanless has written to Justice Secretary Liz Truss to ask why the measure has been delayed and demanding it is brought into force immediately.
He said: "In too many cases the police have been left powerless to take action to protect children who are increasingly being targeted by abusers online.
"This new offence was supposed to mean that the law could be brought to bear on anyone who grooms children online.
"The public have backed our campaign, Parliament has agreed to it and Scotland shows that young victims are bravely coming forward and beginning to reveal the sickening numbers of adults targeting children for abuse, so we cannot understand why the Government is dragging its feet.
"It is an unacceptable and baffling delay in equipping police in England and Wales in the battle against criminals who are intent on targeting children."
Victims Commissioner Baroness Newlove said the legislation should be put in place "without further delay".
She said: "It is not appropriate - nor morally right - that some children continue to endure sexual communication from adults while the Government considers whether to introduce this law."
A fact sheet published by the Ministry of Justice in 2015 said the UK's laws to protect children are robust but it is vital to "remain responsive to changes and developments".
It added: "This is particularly relevant to changes in technology and communications, which along with bringing major benefits to society, have given potential offenders new ways of contacting children to encourage or prepare acts of abuse."
The document said Section 67 of the Act "creates a new offence of sexual communication with a child which will help ensure that young people are fully protected by the law and allow the authorities to intervene earlier to prevent more serious offending against children".
It said the offence, which carries a maximum prison sentence of two years, applies only where the defendant can be shown to have acted "for the purpose of obtaining sexual gratification".
It went on: "Ordinary social or educational interactions between children and adults, or communications between young people themselves, will not be caught by the offence."