His Majesty's Inspectorate of Constabulary and Fire & Rescue Services (HMICFRS) said it had serious concerns about the force's performance in this area, saying it lacked understanding of the "nature and scale of child exploitation" which was a "significant barrier" to being able to address the problem.

In findings published today, the watchdog found the force's response to the criminal and sexual exploitation of children was "not currently effective" and not enough was being done to protect victims.

In the wake of the report, the Met apologised to the children and families it had let down and said it was taking "significant steps" to improve

Among the other "serious concerns" HMICFRS inspectors found were officers and staff using "victim-blaming language" and a "frequently poor" response when children go missing regularly, with officers and staff "simply waiting for them to turn up".

It also said there were delays in launching and progressing investigations, with many "missed opportunities" to identify suspects and disrupt their activity, leaving children exposed to risk.

Of 244 investigations examined, more than half were graded as inadequate.

Inspectors found 22 investigations contained victim-blaming language which the watchdog estimated amounted to "12 in every 100 children being in some way blamed for the abuse they suffered".

They found examples including a 14-year-old girl being described as "seeking out sex with older men", a 15-year-old girl being referred to as "engaged in sex work", and a 12-year-old girl who had been raped branded as "sexually active with older men".

"Worryingly, we didn't see any evidence that supervisors or managers challenged this language. In fact, in one of our interviews with a detective inspector, they spoke of children being promiscuous," the report added.

Language in some crime reports also indicated officers were encouraging children "not to pursue a complaint instead of offering support and reassurance", and in some cases there was no evidence that an officer had even spoken to the child in person.

HMICFRS made a total of 11 recommendations for improvement including following all reasonable lines of enquiry to identify suspects in child exploitation cases as well as stepping up efforts with other public bodies to stop children from going missing and finding them quicker.

Better training was also needed, while officers and staff of all ranks should be told to challenge victim-blaming language.

Inspector of Constabulary Lee Freeman said: "It is particularly concerning that the Metropolitan Police Service isn't doing enough when children are suffering from, or at risk of, exploitation.

"The force should make sure that it fully understands the risks to children, and that officers and staff are equipped to identify and tackle those risks effectively, so no child is left unprotected.

"The Met has already committed to increasing the number of officers in some teams dealing with child exploitation. For the benefit of London's children, the force should implement our recommendations in full and without delay."

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Children's charity the NSPCC said the report "paints a very concerning picture of the Metropolitan Police's response to child sexual exploitation".

It called on the force to bring in the "urgent and systemic changes" highlighted, adding that there also needed to be "national leadership to move the dial on how society responds to child sexual abuse".

Between August and September last year, 202 missing children were graded as high risk. This rose to 398 between December and January, according to the Met.