IT’S 6.30pm on Friday in Blackburn town centre and groups of teenagers gather on Darwen Street.

Some of the youngsters are still in their school uniform. They look like they are waiting for somebody.

Then, as we watch from a discreet distance, one group of teenage boys and girls are met by a smiling man in a tracksuit top.

Meanwhile, on a nearby side street, another man opens an unmarked door from the inside and peers out, making sure no-one is watching.

Then the children are led in single file to the doorway.

The first man lets the group go in one by one, but he doesn’t see the Lancashire Telegraph photographer snapping away.

He then closes the door and runs away.

According to police, these are the hallmarks of the operation of an illegal shisha den.

Officers believe the children taken inside a den will pay around £5 per session.

Several hours later the children emerged.

The Lancashire Telegraph was unable to speak to them due to guidelines on approaching children under 16 without parental consent.

The Lancashire Telegraph has passed the information to the authorities.