As the Government prepares a clampdown on the unaccompanied arrivals following a 67 per cent increase in their numbers, solicitors and refugee workers described the conditions which forced them to flee their homelands.
Tim Kirkhope, the Home Office minister responsible for immigration, condemned these children's parents for sending them to an "uncertain future", and said he believed many were economic migrants sent to Britain because their families could not support them.
Numbers are expected to top 600 by the end of the year, Mr Kirkhope said, at an estimated annual cost to the taxpayer of pounds 12m.
But refugee workers and solicitors said that although poverty was a factor, many young people faced conscription or risked physical assault at home.
In families already devastated by civil unrest or fighting, often the eldest son would be sent to safety to ensure the family line was preserved.
Peter Bartram, a solicitor whose practice is near Heathrow airport, said they had seen youngsters from countries such as Afghanistan who had already seen frontline action.
Official figures showed that famine and civil war have a significant impact on numbers. Mr Bartram noted increases from Eritrea during its war and from Sierra Leone during rebel uprisings.
Mr Bartram said: "Even if they haven't actually been in personal danger, their family has often suffered tragedies. They are often very, very isolated . . . arriving here, they are in a completely alien culture." Some even had no idea which country they were in.
The majority are around the age of 16 and few are younger than 14. Terry Smith, of the children's division of the Refugee Council, said that the increase was undoubted but also marked better identification procedures by immigration officials.
As soon as lone arrivals are identified, they become the responsibility of social services. Roy Mills - spokesman for Hillingdon council, which covers Heathrow - said they at present have 144 children under 18 costing the authority pounds 2.8m a year. Unless a relative was traced in Britain, most then remain in council care.