Children as young as six are being sold and then smuggled into Britain to work as child prostitutes in paedophile brothels.

An investigation by the The Observer says it has evidence that the children from developing countries are being sold by their families and kept prisoner in brothels where clients pay up to £500 for 30 minutes with a child.

The rumours have been circulating for some time about the trend but police have so far been unable to find evidence because the children are constantly supervised, said the report.

But some of the children have managed to escape from the brothels and are now wandering London, homeless, addicted to drugs and too terrified to seek help.

Detective Inspector Paul Holmes, head of Scotland Yard's drugs and vice unit said it was the worse child prostitution problem they had encountered.

The Observer's report was followed up yesterday in the Guardian which looked at the plight of one 14-year-old Nigerian girl sold six months ago into international sex slavery by her father and who was now now addicted to heroin and crack cocaine.

She said she was taken by her new "owners" to a flat in London where there were five other girls from various countries aged from six to 18 and ended up getting hooked on drugs to ease the pain she felt.

After escaping from the brothel, she now spends the nights walking the streets in East London stopping cars because she needs the money and living in fear in case her "owners" find her and kill her.