Police have travelled with drivers on some routes

Over recent months a driver has been stabbed, another attacked with a baseball bat and a passenger has lost an eye in separate violent incidents.

As a result police have accompanied drivers on some journeys and CCTV cameras installed on several buses.

First Mainline managing director Gary Nolan said: "We will do all we can to make sure our staff are not vulnerable. We'll do what we can to support them.

"All we are asking is that we get all the help we can from the public. We have to get someone for doing this and press charges and make it stick."

Police say the 25 March attack was on a 29-year-old bus driver from Shiregreen, who was heading through Burngreave on the number 47 service at 1900 GMT.

He was shot at close range in the face through his open cab window. A pellet lodged near his eye.

Stiffer sentences

A South Yorkshire Police spokesman said: "At 1746 GMT on 26 March we had reports of another incident in which passengers reported two or three youths firing an airgun at a bus as it was travelling along Queen's Road.

"Luckily no-one was hurt that time."

The Transport and General Workers Union, which represents the Sheffield drivers, wants risk assessments, stiffer sentences for offenders, and better police resources.

But the South Yorkshire Police spokesman said: "This has to be tackled jointly.

"There will be some targeted, high-profile policing, but it just cannot mean that whenever you get on a bus in Sheffield you see a police officer."