Union leader Paddy Lillis has called for people to “keep their cool” with shop workers, following abuse on the discounting day in previous years.

A Usdaw survey of shopworkers in 2014 revealed a two-thirds increase in incidents of threats, violence and verbal abuse against retail staff on Black Friday, so the union set out to minimise any future abuse.

Lillis said: “Our members have had real concerns about Black Friday. After two years of unprecedented scenes of mayhem in some stores, as bargain hunting turned into a frenzy, we discussed safety issues with retailers.”