A ban on alcohol on London's transport system comes into force on Sunday, designed to make buses, Tubes and trains safer for the public, but with unions warning staff could be put in greater danger instead.

The ban was a key manifesto pledge of new mayor Boris Johnson's election campaign, and just days after his victory over Ken Livingstone, he announced plans to enact the measure.

"I'm determined to improve the safety and security of public transport in London and create a better environment for the millions of Londoners who rely on it," Johnson said.

"I firmly believe that if we drive out so called minor crime then we will be able to get a firm grip on more serious crime."

The ban will apply to buses, underground trains, trams and stations.

However the RMT union called the booze ban "half-baked" and said it could lead to more assaults on Tube staff who will be in the front line against "aggressive drunken behaviour".

"The ban has been poorly thought through, is being implemented in haste and could put our members in danger," said RMT General Secretary Bob Crow.

"Violence against Tube staff is already a major problem, particularly from people who have been drinking, but now our members will be expected to approach people drinking and stop them or even remove them from the train or station."

Tackling crime, particularly serious violence among young people, was one of the main planks of Johnson's election campaign and he has already vowed to put it at the forefront of his mayoralty.

"Public drinking and the behaviour sometimes associated with it can, and does, deeply affect people's ability to enjoy public spaces," said Don Shenker, Chief Executive of Alcohol Concern.

"Taking a firm approach to public drinking in this way sends a strong message that public drunkenness is socially unacceptable and will support both the public and transport staff."