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"I have never seen that much blood" the team leader from a Co-op store in Greater Manchester said.

"My colleague had attempted to stop a shoplifter... a bottle smashed on the floor and the shoplifter used this as a weapon."

This "rising tide of violence" against shop staff has prompted retailers to write to the government calling for more to be done to tackle the problem.

The government launched a consultation on attacks on store staff in April.

It closes on Friday and in response, the retailers have submitted a letter to ministers including the home secretary calling for "meaningful change that will reduce levels of violence and abuse".

The signatories include the bosses of Sainsbury's, John Lewis Partnership, the Co-op, and Marks and Spencer, along with the British Retail Consortium (BRC) and the Association of Convenience Stores (ACS), the Charity Retail Association and the shop workers' union Usdaw.

According to the letter:

115 workers are attacked every day in the UK

Almost 10,000 incidents of violence in convenience stores in the past 12 months

On average a shop worker is "abused, threatened or assaulted" 21 times a year

The letter said this evidence "highlights one inescapable fact - violence against retail colleagues is a hugely problematic and serious area of crime, with weapons, particularly knives, increasingly significant".

"This violence is commonly triggered by shop workers delivering what the state asks of them: enforcing age restriction policies or refusing to serve intoxicated customers, or dealing with shop thieves, who might be carrying weapons."

The retailers recommend:

Tougher sentences for those who attack shop workers

Change to the out-of-court system such as fixed penalty notices which signatories say are failing to have an impact on reoffending

A full review into the response of police forces to incidents of violence in the retail sector

ACS chief executive James Lowman said: "Retailers and staff that have been subjected to abuse often give up on reporting crimes to the police because nothing is done, and that needs to change.

"We need fundamental reform of the justice system to deter criminals from committing lower level offences, more consistent police response to show retailers that they take incidents of violence and abuse seriously, and ultimately tougher sentences to tackle reoffending rates when the worst does happen."

'Horrific'

The Home Office said: "Shop workers have the right to feel safe at work and for them to experience violence or abuse is totally unacceptable.

"That is why we launched a call for evidence in April to enable us to learn more about the scale and extent of this issue and inform our response."

The Co-op encouraged its staff to submit responses to the Home Office consultation.

The staff member who witnessed the aftermath of the attack on a colleague with a bottle was one of the respondents, and wrote: "The offender was caught by police and sentenced, but I know he is back out in the community and offending by recently shoplifting from a local store.

"The image of that day was quite horrific and one I still think about, but I can't imagine the impact it had on my colleague who has since left the business.."