National criminal gangs have been homing in on south Essex carrying out violent armed robberies on security guards.

The south of the county has suffered eight such crimes in the past four months, including four in December alone.

Hundreds of thousands of pounds has been stolen by gangs targeting security guards delivering and picking up cash from banks and shops.

Last Friday a guard was knocked to the ground by two robbers as he carried a cash box to the Abbey bank, in Broadway Pitsea.

Just days earlier, robbers carrying a handgun held up a Securicor security guard as he made a cash delivery to Barclays Bank, in London Road, Benfleet.

Det Chief Insp Keith Dobson, of Essex Police, said: "It is quite clear there are a number of teams operating throughout the length and breadth of Britain with specific criminal operators based here in Essex and in surrounding counties.

"The robberies are committed by the home teams, but also by those who travel in and out of Essex to carry out the attacks."

He added: "We are liaising with neighbouring forces in order to identify common themes and links between gangs, focusing on patterns in a bid to prevent further strikes and to arrest the perpetrators."

The recent surge in the number of security guard robberies has been attributed to bumper Christmas shop takings.

Mr Dobson said: "There was an increase at Christmas purely because there is more money on the streets at this time of year.

"Shoppers were withdrawing money to buy presents and so the banks, stores and ATMs need restocking on a more frequent basis."

He added: "There have been no specific, targeted areas across Essex with all parts affected by this form of crime. Criminal gangs are known to move around the county and indeed, the country, in a bid to evade capture and put police off their scent."

The recent spate of robberies by organised gangs has prompted local low-level criminals to attempt the crime.

Mr Dobson said: "We have seen pairs of young men walking up to the guards and trying to snatch the cash boxes from their hands. Pillion passengers have tried to grab the box while their motorcyclist accomplice has ridden at the guard at high speed."