AUTHORITIES have issued a warning to users of "hook-up" apps such as Grindr that they must take responsibility for checking people they meet are above the age of consent.

Police said a child "should never be blamed" in a case of apparent grooming, regardless of how the two people meet.

"Hook-up" apps have become popular among people looking for casual sex online because they give the specific location of each user. The maker of Grindr and Blendr - which are marketed for gay and straight people respectively - claims they are used by around 250 million adults worldwide.

The UK's National Crime Agency said while it did not collect specific figures relating to such apps, it had seen a rise in calls referring to them.

NCA's Jonathan Baggaley said: "The law is very clear ... the adult is always the one who has the responsibility. A child should never be blamed."

The NSPCC's Claire Lilley told the BBC the apps' age-restricting terms and conditions were not being enforced, "and as a result children are being put at risk of serious harm".

The company behind Blendr and Grindr issued a statement saying: "We do our best to ensure all users follow our strict terms-of-service policy that require users to be at a minimum age of 18."