The Home Office rejected an offer of expert help to establish the ages of refugees seeking to come to the UK from the so-called Jungle camp in Calais, it has been claimed.
Specialist social workers were offered to the Home Office in August to help prepare for the arrival of refugees from the controversial French camp, which is set to be cleared this week.
But the Local Government Association (LGA) said officials did not take up the offer and only started asking for specialist help on Friday as concerns were raised by some MPs about the age of the refugees arriving in Britain.
The Sunday Telegraph said councils had offered to send social workers to Calais to carry out age checks but were ignored.
David Simmonds, chairman of the LGA's asylum, refugee and migration taskforce told the newspaper: "We made the offer in August and the Home Office didn't take it up at the time. They only started asking for social workers with age assessment experience on Friday."
He added: "The offer was not taken up quickly enough. I understand that on Friday the Home Office started asking Kent for social workers with experience in age assessment.
"But we offered our help three months ago. I am aware they were trying to talk to people on Friday to get help after all."
A Home Office source insisted the support had not been needed when it was offered in August.
Some of the first wave of arrivals this week provoked speculation over their ages amid suggestions some appeared to look much older than teenagers and Tory MP David Davies suggested using dental checks to establish how old they were.
Screens have since been used to keep the refugees hidden from public view after arriving at a Home Office building in Croydon, south London, from the muddy, rat-infested slum in northern France.
Dozens of young migrants have arrived in the UK in recent days, including the first group of vulnerable unaccompanied children without links to Britain under the landmark Dubs amendment.
Previously all the young refugees who have arrived in Britain have been brought under the Dublin regulations, which require the children to have family resident in the UK.
On the latest arrivals, Bishop Jonathan Clark, spokesman for Citizens UK, said "the most vulnerable" were "at last being transferred to Britain under the provisions of the Dubs amendment, including many young girls".
Demolition teams are preparing to move into the Jungle on Monday to clear the estimated 6,500 inhabitants who will be relocated to reception centres across France.
British members of anti-capitalist protest group No Borders will head to Calais in an attempt to block the demolition of the camp, The Sunday Times reported.
At a meeting in south-east London last Sunday, one activist told the paper that "lots of us will be going down" and warned people should not join them unless they "understood the risks".
In January, British anarchists were among those reported to be stirring up trouble in Calais when migrants and protesters stormed the port and boarded a ferry.