Vigilante paedophile hunters who trap online child abusers have been warned to cease their “sting” operations by police.

Detectives with West Yorkshire Police are understood to have written to groups that confronted alleged paedophiles and broadcast the results online.

Officers say the groups’ activities risks interfering with ongoing official police operations, such as surveillance, and that “evidence” obtained could be inadmissible in court.

At least one group, Protecting Innocent Kids Online (PIKO), has announced via its Facebook page that it will not publicly broadcast its stings in future.

However it did not agree to reduce its operations.

A letter sent by West Yorkshire Police warning paedophile hunters who trap alleged offenders to cease their sting operations.

The letter confirms that West Yorkshire Police is unable to sanction activities regarding the identification of potential child sex abusers and adds: “As a result we request that you cease from any similar activity in the future, namely posing as a child on the internet, engaging with potential offenders and arranging to meet them.”

Hunters are also warned that targeting individuals “could amount to harassment” and that their human rights might be infringed.

“We do stress that certain activities carried out by these groups could undermine police investigations and leave the individuals themselves open to prosecution, and advise them of these and other matters.”

There have been several high-profile instances of vigilante justice in recent months in the region.

In November Mark Shah arranged to meet a 12-year-old girl at Dewsbury Railway Station after secretly grooming her online. The girl, “Summer”, was actually a member of the vigilante group Silent Justice. He was confronted by paedophile hunters and arrested by police.

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Shah, 43, of Stonehyrst Avenue, Crackenedge, Dewsbury, was jailed for three years two months and ordered to register indefinitely as a sex offender.

Paedophile Mark Shah, who was caught in a "snare" operation at Dewsbury Rail Station by vigilante paedophile hunters.

Christopher Watts, from Halifax, was involved in Facebook sex chats with members of a paedophile hunting group posing as under-age girls.

Members of a group called Sub Division Hunters alerted police to Watts’ activities last October when they confronted him about conversations he had been having with four of their “decoys.”

Watts, 35, of Concrete Street, Lee Mount, avoided prison but was banned from contacting any females under 16 via the internet for 15 years and given a community order to tackle his behaviour.

In its statement Team PIKO said it would not publicly broadcast stings in future.

Instead it would live stream to a closed secret group containing only hunters and decoys “for the sole purpose of identifying if any other teams have evidence on the predator being stung.”

It added that a separate device will be used to record stings in order to pass evidence to the police.

It promised to inform the public and followers of its page when members are en-route to a sting and then update live to its public page following the sting with details of what happened in what area and the police’s actions.

“No name and or picture of the predator will be released publicly until a conviction takes place but the public will be informed of the process and outcome throughout.

“There is a lot of attention on hunting teams at present from the authorities and media organisations, and we need to ensure that we change with the times.”

Supt Darren Minton, of West Yorkshire Police’s Safeguarding Central Governance Unit, said: “As referenced in the letter, West Yorkshire Police share the concerns of groups regarding the internet activity of potential child abusers and encourage members of the public to report illegal activity.”