Police have set up fake websites to catch people accessing child porn, the National Crime Squad (NCS) has said.
The NCS has welcomed the blocking of child porn websites
Detectives collect people's personal details entered into fake sites which appear when key words are searched for.
The NCS told BBC News Online about police techniques in the fight against online porn, after BT revealed how widespread UK web paedophilia was.
BT said its new Clean Feed system is blocking an average of 10,000 attempts each day to access child porn.
It bars access to certain sites and presents a message to users which reads "Website not found".
The telecommunications company said in its first three weeks the new system registered nearly 250,000 attempts to view web pages containing images of child pornography.
The figures provide the first firm indication of the extent of web paedophilia.
Internet service providers pass on concerns about particular users to the Internet Watch Foundation (IWF), who may then refer the case to the relevant police force and ultimately the NCS.
NCS spokeswoman Jackie Bennett told BBC News Online: "We do not block sites but we liaise very closely with the industry, from service providers to telecommunication companies and the IWF, as well as child protection agencies.
"We try to stop the supply of images and, through the industry, the demand can be stopped."
Police forces in the UK and elsewhere in the world are exploring various ways of clamping down on offenders.
In December 2003 it emerged that a web sting had been set up by the NCS, who worked with the FBI, Interpol, the Royal Canadian Mounted Police and the Australian HI-Tech Crime Centre.
The online operation, known as Operation Pin, targets offenders by setting up fake websites that collect details of people wanting to look at child porn.
Law enforcement agencies have worked with search engine operators to ensure that the fake sites appear when a person looks for certain keywords.
The aim is to prevent people joining the more clandestine community of experienced paedophiles.
As yet it is unclear how many offenders have been caught as a result of this approach.
The NCS spokeswoman said every single image of child pornography was a case of child abuse and unacceptable to society.
"We must do everything that we can to clamp down on these horrendous crimes," she said.
Chat room patrols
She pointed to the work of the Virtual Global Task Force (VGTF), as an example of the way in which enforcement agencies worldwide are working together.
In June it proposed that police around the world should manually "listen in" to online conversations 24 hours a day, seven days a week.
Under the proposals, police officers would visit selected chat rooms and make themselves visible to users, perhaps by displaying a form of recognisable logo.
BT is only one of the main service providers in the UK and police leaders are now calling for others to block paedophile websites.