Image caption The NSPCC said up to 35,000 indecent images of children were found by police every day

The number of detected crimes of people accessing illegal images of children has gone up by 48% in four years, according to research by BBC News.

The figures are for England and Wales and show the increase between 2007-11.

A charity which works with offenders to stop them accessing images said there were many more offenders and that it was impossible to arrest everyone.

The Home Office said it was working with the police and industry to make the internet a safer place.

The figures were obtained under the Freedom of Information Act from the 34 police forces in England and Wales that were able to provide data for the crimes of possession of an indecent or pseudo photograph of a child and possessing prohibited images of children.

In 2007, 919 crimes were detected by the police, however in 2011, this had risen to 1,362.

For crimes that were reported to the police, the increase was 46%.

The figures were analysed and verified by the chairman of the Crime and Justice Statistics Network, Professor Allan Brimicombe.

'Not a few sick men'

The NSPCC said on average, up to 35,000 indecent images of children were found every day by police forces and that some offenders had been caught with more than one million images.

In 1990 - before the internet took off - the charity said there were just 7,000 hard copy images in circulation.

We have to recognise the limited potential of law enforcement to fully deal with this problem Donald Findlater, Lucy Faithfull Foundation Can child porn users be treated?

Jon Brown, head of the charity's sexual abuse programme, said the challenge of eliminating this type of crime was "as significant as ever".

"We need to ensure that it doesn't get created in the first place, so we need to put significant effort in prevention and offering a deterrent for offenders."

He said he had noticed the children being abused had changed in recent years. As broadband has become more prevalent in Africa, he said more children from that continent were being abused and put online.

Mr Brown added that there was also a decrease in the age of children being abused and that more children were being encouraged to do sexual activities through webcams which were then filmed and uploaded online rather than being groomed to meet up.

"The inhibitions are too few, especially if men are in a room by themselves - it's too easy," he said.

"We need to be asking what is the male psychology that makes them view this imagery? It's not just a few sick men, it's a much larger number.

"As a society we haven't got our heads around that, we need to recognise this and have a rational and sensible conversation rather than see them as monsters or beasts."

'Danger to children'

Donald Findlater from the Lucy Faithfull Foundation, a child protection charity, said the problem was more widespread than police figures show.

"We have to recognise the limited potential of law enforcement to fully deal with this problem," he said.

"We have to provide far better ways to prevent the crime rather than assume arrests are the way out."

He said warning notices needed to be put on the internet so that if someone searched for certain key words, a warning would come up asking if the person realised the impact this search would on their lives as they could lose their liberty, children, partner and job.

Norway has such a system in place.

"That would be one way of warning someone off. Today it might be a curiosity, but if they do it for longer they could become a danger to children," he said.

Peter Davies, chief executive at the Child Exploitation and Online Protection (Ceop) Centre and ACPO lead police officer for child abuse investigations, said the volume of indecent images had increased "dramatically" in recent years and now runs into millions.

"Ceop, police forces in the UK, the internet service providers and international law enforcement are becoming increasingly successful at targeting offenders and working closer than ever before to protect children from harm caused by those who have a sexual interest in them," he said.

A Home Office spokesperson said: "We already expect companies providing internet services to use the Internet Watch Foundation list to block access to illegal images of child sexual abuse.

"We are also clear that if child abuse takes place, it must be thoroughly and properly investigated and those responsible arrested and brought to justice."