Street cleaners have been shot at as they go about their work.

Bradford Council said it was becoming increasingly concerned about the level of violence used against all its staff as they carried out their duties.

Cleaners in some areas are now working in gangs of three or four for protection, and will even only go to some streets very early in the morning to avoid potential attacks.

The workers have been fired on by airguns in separate incidents in parts of the district, including Slaymaker Lane, at Oakworth.

Staff escaped unhurt but the shots shattered the windscreens of their vehicles, leaving workers badly shaken.

Damian Fisher, principal waste management officer for street cleansing at Bradford Council, said the level of violence directed towards staff had become a major concern.

"Luckily the workers weren't hit but it could have been deadly," he said. "It is extremely worrying because this is something we haven't come across before. I just hope it isn't the start of a new trend."

He said street cleaners had become the targets for physical and verbal abuse and were repeatedly being picked on in certain areas of Bradford.

"People see street cleaners as not being respected in society and think they can treat them how they like," he said. "They really have to put up with a lot and need to be quite tolerant sometimes, but it seems to be getting worse."

Working patterns have had to be altered in parts of Bradford to account for the level of violence directed towards cleansing teams.

"There are some areas where we have to send gangs of three and four street cleaners because it isn't safe for them to be there alone," he said. "In the worst areas we clean early morning when people are still in bed, but don't go back in the afternoon because it is just too dangerous."

Working practices had to be reviewed last year after 23 streets were declared no-go zones when a woman street cleaner was pulled from her street sweeping vehicle and held at screwdriver point in Amberley Street, Bradford Moor, where one of the street sweepers was shot at last month.

Mr Fisher said: "There are no areas at the moment where we refuse to go to as such. We just encourage staff to work in teams."

He said the nature of violent incidents was getting worse, despite a decrease in the number of assaults reported by cleansing staff.

"There has actually been a reduction in the number of incidents reported," he said. "But air rifle attacks are something we have not experienced before."

Ray Alderman, GMB union convenor for Bradford Council, said: "We are very concerned about violence against the workforce and we are always coming across members who have been physically and verbally abused.

He said people forgot that street cleaners were human beings who had the right to do their jobs in peace.

"I think people just see council workers and decide to have a go, but they shouldn't have to put up with that sort of thing," he said.

Police are still investigating the incident in Oakworth, and would like anyone with information to call them on 0845 6060606.