Undercover police officers are travelling on Brighton and Hove buses to combat robberies and assaults on drivers.

Uniformed officers and specials will also "ride shotgun" to protect staff.

Police and bus chiefs met yesterday to launch the initiative - and just 24 hours later two more attacks had happened.

The latest came this morning when a group of youths abused and spat on a driver at the bus terminal in West Street, Rottingdean.

Police were called but it was not classed as an emergency and it was some time before officers arrived.

A second bus at the terminal left late because of the fracas and a passenger who got on later at Woodingdean demanded a free ride as compensation.

The driver insisted on payment. As the passenger got off the bus in Sutherland Road, Brighton, he punched the driver in the face.

The driver was not seriously hurt.

Last night two masked youths armed with a knife tried to rob a driver in Hillside, Moulsecoomb, Brighton, just after 11pm.

A teenager on the bus helped foil the raid by opening an emergency door. The alarm scared the robbers, who fled empty-handed.

Roger French, managing director of Brighton and Hove Bus and Coach Company, said: "These incidents are utterly deplorable and I am delighted the police are taking action."

There has been a spate of robberies on buses in recent weeks.

The driver of one empty vehicle was threatened with a knife in Queen's Park Road, Brighton, on March 3. The raider escaped with a small amount of cash.

Police think the thief may be the same man who robbed the driver of a No 7 bus in Donald Hall Road, Brighton, on February 28.

A knife was used and again the man escaped with cash. The driver and three passengers suffered shock but were unhurt.

Another driver had cash stolen two weeks earlier but police are not connecting the crime.

It happened in Swanborough Drive, Whitehawk, when two men grabbed a cash bag from the driver.

Detective Chief Inspector Martin Cheeseman, head of Brighton CID, said: "A concerted effort to improve security, including the use of plain-clothed officers and specials, is being launched."

One angry driver said busmen were threatening to take their vehicles off the roads to demand more protection.

But GMB union representative Gary Smith said there were no plans for industrial action.