Police officers investigating hundreds of child sex abuse cases are at breaking point psychologically with many suffering exhaustion, secondary trauma and stress, a leading psychologist has warned.

Dr Noreen Tehrani, who advises specialist child abuse detectives in the Metropolitan, Surrey, Thames Valley and Hampshire forces, added that pressure from Westminster politicians forced police to divert attention from children at risk to historical cases.

"They are just completely inundated with work, they are beginning to collapse. What I am getting are more and more exhausted officers. There aren't enough officers in these specialist teams and they are overwhelmed," Tehrani said.

Tehrani said officers were on the point of collapse, with many going off sick as a growing number of historical claims of abuse increased pressure on already busy teams. She told the Guardian that she would be writing to David Cameron and Theresa May, the home secretary, to express her deep concern at the pressures the teams are under.

The psychologist's work means that she sees six officers a day, four times a week, in work that is seen as a necessary support for police officers handling what are often traumatic child abuse cases. She said that she was speaking out because the officers were not able in the current climate to talk themselves of the pressures they were under.

Tehrani said: "I am seeing officers with secondary trauma, with PTSD [Post-traumatic stress disorder], with stress. They have to interview vulnerable children or adults, they have to go through all of the physical details of what has happened to them, they have to test the evidence. These are the people that politicians are demanding more and more of, and I don't know how much more they will be able to take."

This week May said the police were investigating a shocking number of child abuse claims from across the country. Allegations have increased dramatically following the exposure of celebrities such as Jimmy Savile, Rolf Harris and Stuart Hall.

Officers are dealing with hundreds of cases involving abuse in the past in institutions including schools, churches, children's homes and a number of allegations relating to high profile people. Their workload is likely to increase further with the establishment of the wide ranging inquiry led by Lady Butler-Sloss, announced by ministers earlier in the week.

Tehrani said many had spoken to her of their concern at being diverted from current cases of abuse to investigate historical cases as a result of clamour from politicians and the media over rumours of an alleged network of powerful abusers who operated in the past.

Statistics show that the vast majority of child sexual abuse takes place in the home.

Strangers are responsible for approximately 10% of child abuse cases, while 30% of abusers are related to the child – mostly father, stepfather, uncle or cousins. About 60% of abusers are other acquaintances of the child.

Tehrani added that officers felt "considerable frustration" because the political climate meant that important current cases could not be dealt with because "they are being diverted to dealing with these historic cases. The thing about historic abuse in the main is that the abuse has stopped, there are not children at risk now who need to be removed from the situation."

One senior source close to the Met child abuse command said: "They are under considerable pressure with the increase in workload and the whole command suffers because of it. But as long as victims are still getting a good service I think the officers will manage."

Two weeks ago Tehrani stepped in to help an officer who was suffering secondary trauma from the work he was doing, and was unable to give evidence in person in a sexual abuse case.

The psychologist persuaded the judge to allow the officer to give his evidence without being present in court.

"The judge asked if I wanted to say anything, and I told him we have got some really dedicated officers doing some of the most difficult police work that there could be, and we need to look after them. I think someone has to speak out."