Police are urging shopkeepers not to sell eggs and flour to under-16s ahead of Halloween amid fears pranksters might use them to cause mischief.
Officers said they launched the crackdown in King's Cross in central London after youths pelted homes with homemade concoctions in trick or treat pranks in previous years.
The Safer Neighbourhood Team (SNT) said vulnerable and elderly residents have been targeted.
In a letter, pinned up to a shop front in King's Cross, officers asked shopkeepers to volunteer not to sell the household staples to under-16s in the week before Halloween.
It reads: "I would like to ask that you refrain from selling eggs and flour to children under the age of 16 for the week prior to Halloween (i.e. from 22nd October 2015).
"This is because over the past few years we have experienced problems in the lead up to Halloween with youths throwing eggs and flour at residents houses (particularly those elderly and vulnerable) under the guise of 'trick or treat'.
"The King's Cross Safer Neighbourhood Team will be patrolling until later on Halloween (31 October) to deter any such incidents and to deal swiftly and effectively with any that do take place."
Labour councillor for King's Cross Jonathan Simpson dismissed suggestions the initiative is an overreaction, and said it showed that police are being proactive in tackling anti-social behaviour.
He said: "The police don't send out letters lightly.
"I don't have a problem with it. It may inconvenience some young people but it is probably a week or so and I would rather that than have a vulnerable or elderly resident attacked.
"I wouldn't want an elderly or vulnerable resident to be faced being pelted in a violent way at any time of year. It is a way of preventing that."