Scotland Yard's sex crime squad was left with dozens of jobs unfilled despite a surge in claims of child abuse, a report has found.
The number of alleged child rapes and sexual assaults has risen by a third in London in the past five years, with a 10% jump in claims last year, but at the end of 2013 several posts in the force's Sexual Offences, Exploitation and Child Abuse Command remained empty.
On paper, the number of officers dedicated to investigating sex crimes rose by just over a fifth in the same five years, but this did not reflect the number of jobs left unfilled, the London Assembly found.
More than 50 jobs were vacant in September last year, and 150 officers have been given other duties such as working on high profile sex crime investigation Operation Yewtree, while "a large proportion" of women were on maternity leave and their jobs had not been covered.
The force said that some officers were working for the teams but were not recorded in workforce numbers, although Assistant Commissioner Mark Rowley acknowledged this was a "massively pressurised area".
In March this year, he said 40 officers would be brought into the team from the homicide command and bosses were looking for another 75 to plug gaps.
The report also predicted that the number of referrals made to the Met of cases of alleged child abuse, currently in the hundreds, could increase to 2,000 or 3,000 because of raised awareness, and it questioned whether the force had the capacity to deal with this.
Deputy Chair of the Police and Crime Committee Caroline Pidgeon said: "While the number of allegations of child rape and sexual assault make horrendous reading it is encouraging that more people now feel confident enough to report these horrific crimes to the police.
"When they do so the Met must have sufficient resources in place to ensure robust enquiries regardless of whether the case involved a celebrity many years ago or a neighbour or relative just yesterday.
"Our investigation found many encouraging improvements in the way the Met approach their child safeguarding responsibilities and how they and many other agencies are working together to protect London's children.
"Those improvements must not be put at risk by significantly increasing the workloads of officers who have to deal with difficult investigations into harrowing cases."
In the newly-published report, assembly members warned that the Sexual Offences, Exploitation and Child Abuse Command was being placed under serious strain, particularly following the increase in sex crime allegations since December 2012.
It said: " In the last two years, allegations, investigations and detections of abuse against children have risen.
"The Met has increased the Sexual Offences, Exploitation and Child Abuse Command's (SOECA) staffing to meet this increase, but evidence suggests that the command remains seriously under-resourced."
From 2012/13 to 2013/14 the number of child rape allegations in the capital increased by 14% - from 511 to 583 - and sexual assault claims by 13% - from 1,599 to 1,803.
But the number of crimes that were successfully dealt with had also increased, with 2,268 sanction detections in the year to November 2013, a rise of more than 10% compared to the previous year.
The report found that child protection strategies higher up were not always filtering down to officers on the beat, with the Children's Society claiming that police awareness and knowledge could "depend on who answers the phone".
It said: "We heard that, generally, Met officers lack a clear understanding of what constitutes child sexual exploitation (CSE).
"We were told that borough-based officers do not always have the skills, training and awareness to enable them to recognise the signs of CSE and other forms of child sexual abuse.
"The Committee is therefore concerned that the Met may not be fully able to identify children who are at risk, and to take effective action."
The report also found that while the Met is taking female genital mutilation (FGM) seriously, it "could do more within communities to end FGM: in particular, raising awareness of the legal and health implications of the practice with community leaders, faith groups and schools".
Investigators were told: "In some instances, the Met lacks understanding of key cultural practices and what FGM is.
"As a result, it is ill-equipped to identify and investigate cases of FGM."
The force has already warned that a lack of tip-offs from health and education workers has hindered efforts to uncover more cases.
Scotland Yard said: "We are pleased the Police and Crime Committee has acknowledged the improvements we have made in protecting children, including our work with partner agencies.
"This is a crucial time to ensure we are doing all we can to protect the most vulnerable group in our society. We recognise there are always improvements to be made, and close scrutiny by an external body provides an ideal opportunity to get an outside view on how we are performing."
There are more than 1,130 staff working in the Sexual Offences, Exploitation and Child Abuse Command, and in the face of increased demand 50 detectives have been transferred permanently to the unit from Homicide and Major Crime, and more than 40 officers moved temporarily from other areas.
A statement from the force continued: "At this time a thorough review is ongoing to identify the appropriate staffing levels to meet demand both now and in the future.
"As well as responding to increased non-recent allegations, we are also placing more emphasis on issues such as CSE and FGM. "We will now take time to closely examine the recommendations from this report."