Image copyright File picture/Usdaw Image caption STOCK PICTURE: Many shop workers suffer threats and even assaults from customers, says Usdaw

Jackie McKenzie, 56, has worked at a supermarket petrol station in Bathgate, Scotland for the last 20 years.

During that time, the amount of abuse she has faced while doing her job has been rising.

"I've been verbally abused on a daily basis," she said. "It's getting a bit out of hand to be honest."

She is not alone, according to a new survey, which has found that retail staff are abused, threatened or assaulted on average 21 times a year.

A survey of over 4,000 retail staff by shop workers' union Usdaw, found that around two-thirds have experienced verbal abuse, while 41% were threatened by a customer and nearly 5% were assaulted.

The trade union has been campaigning to stop abusive behaviour towards retail staff for a number of years and in June called on the government to tackle the problem.

"People think that just because we work behind a till there's no reason to respect us," said Michelle Whitehead, 46, a convenience store worker in Wolverhampton.

"It's terrible to say but you get used to being threatened. When someone comes and shouts at you it does affect you. Sometimes you have to walk away from the counter and count till 10 so you don't burst into tears."

Violent attacks

Ms Whitehead, who has been a retail worker for almost three decades, says that incidents used to occur once in a while but now she receives abuse from customers on a weekly basis.

She said she often encounters difficulties when dealing with young people who are underage but seeking to purchase alcohol or cigarettes.

She has also been spat at for refusing to hand over parcels from the post office counter without proof of ID.

Image copyright Mike Kelly Image caption Retail worker Michelle Whitehead says that no one intervenes when customers shout at her

Although neither Ms Whitehead or Ms McKenzie have been assaulted, they have witnessed violent attacks.

Ms McKenzie said one night, while managing the shop on her own, she witnessed a young man run into the convenience store begging for help and a minute later, another boy had run in and started beating him up.

"I shouted to him to stop from behind the counter and pressed the panic button, and the police did come. But by that time the guy had a broken arm and a broken jaw, and the shop was trashed," she said.

The two workers are campaigning for retailers and the government to make changes so retail staff can feel safe while they are at work.

They want signs up in stores telling customers to respect staff, more police on patrol and for retailers to impose a life-time ban on customers who persistently abuse shop workers.

Abusive customers should also have to face criminal charges, they said.

"If that's the only corner shop you can go to, it might make you think if you could have a life-time ban," said Ms Whitehead.