Police said Scream-style masks were not a good idea

Police patrols will be stepped up and officers plan to confiscate masks from "threatening" youths.

Figures show a marked rise in robbery and other offences during Halloween, with "trick-or-treating" often used as a cover by criminals.

Scotland Yard insisted it was not "demonising" young people.

Scream masks

Gangs of youths who dress up deliberately to scare people will be stopped and quizzed by police during the October celebration.

Assistant Commissioner Tim Godwin said police were not targeting children trick-or -treating under adult supervision.

He said the operation was aimed at gangs of youths wearing masks to intimidate people.

"If you are walking around as a group wearing masks, picking people on the street, that has a different impact," he said.

"If you are about 6ft 3in and you have a Scream (film) mask on that has a substantially different impact."

There were almost 250 more robberies than usual in London during the week of Halloween in 2005, according to Scotland Yard.