Basra, after British left.

The full scale of the chaos left behind by British forces in Basra was revealed yesterday as the city’s police chief described a province in the grip of well-armed militias strong enough to overpower security forces and brutal enough to behead women considered not sufficiently Islamic.

As British forces finally handed over security in Basra province, marking the end of 4½ years of control in southern Iraq, Major General Jalil Khalaf, the new police commander, said the occupation had left him with a situation close to mayhem. “They left me militia, they left me gangsters, and they left me all the troubles in the world,” he said in an interview for Guardian Films and ITV.

Khalaf painted a very different picture from that of British officials who, while acknowledging problems in southern Iraq, said yesterday’s handover at Basra airbase was timely and appropriate.

Major General Graham Binns, who led British troops into the city in 2003, said the province had “begun to regain its strength”. He added: “I came to rid Basra of its enemies and I now formally hand Basra back to its friends.”

But in the film, to be broadcast on the Guardian Unlimited website and ITV News, Khalaf lists a catalogue of failings, saying:

· Basra has become so lawless that in the last three months 45 women have been killed for being “immoral” because they were not fully covered or because they may have given birth outside wedlock;

· The British unintentionally rearmed Shia militias by failing to recognise that Iraqi troops were loyal to more than one authority;

· Shia militia are better armed than his men and control Iraq’s main port.

In the interview he said the main problem the Iraqi security forces now faced was the struggle to wrest control back from the militia. He appealed for the British to help him do that: “We need the British to help us to watch our borders - both sea and land and we need their intelligence and air support and to keep training the Iraqi police.”

David Miliband, the foreign secretary, who attended the handover ceremony, acknowledged that the territory was not “a land of milk and honey” and promised Britain would remain a “committed friend” of Iraq.

But he insisted it was the right time to hand back control. “The key conditions for the transfer of security responsibility to the Iraqi security forces are whether they are up to it: do they have the numbers? Do they have the leadership and training to provide leadership for this province? And the answer to those three questions is yes,” he said.

After the handover Des Browne, the defence secretary, praised British forces - 174 of whom have died since the start of the war in March 2003. “Their contribution has been outstanding and their courage inspiring,” he said. A scaled-down UK force will remain in a single base at Basra airport, with a small training mission and a rapid reaction team on “overwatch”.

Britain now has 4,500 troops in Iraq. The prime minister, Gordon Brown, has said numbers would shrink to 2,500 by mid-2008 though those released may be redeployed to Afghanistan.

Khalaf, who has survived 20 assassination attempts since he became police chief six months ago, said Britain’s intentions had been good but misguided. “I don’t think the British meant for this mess to happen. When they disbanded the Iraqi police and military after Saddam fell the people they put in their place were not loyal to the Iraqi government. The British trained and armed these people in the extremist groups and now we are faced with a situation where these police are loyal to their parties not their country.”

He said the most shocking aspect of the breakdown of law and order in Basra was the murder of women for being unIslamic. “They are being killed because they are accused of behaving in an immoral way. When they kill them they put underwear and indecent clothes on them.”

In his office Khalaf showed the Guardian a computer holding the files of 48 unidentified women. “Some of them have even been killed with their children because their killer says that they come out of an adulterous relationship,” he said.

Vince Cable, the acting Lib Dem leader, called for a timetable to bring all British troops home from Iraq, adding: “If we are handing power back to the Iraqis, why are 4,500 British troops needed for what is essentially a training mission?”