Magdalen Bridge will be protected by a ring of steel to stop students throwing themselves to injury and even death on May Day.

The 25ft-high bridge will be shut between 3am and 9am on May Morning and guarded at both ends by a cordon of 40 police and 30 bouncers to prevent a repeat of last year's carnage when 40 students were hurt some seriously jumping into the shallow River Cherwell.

Authorities, including the police, emergency planning teams, paramedics and fire officers decided to close the bridge following fears that after years of relatively minor injuries, someone could jump to their death.

And police have vowed to use "whatever means necessary or appropriate" to prevent anyone breaking the security cordon in an effort to jump, even though the centuries-old tradition is not a criminal offence.

Yesterday police maintained they were not killjoys, but only wanted to prevent serious injury. Oxford police Chief Insp Steph Cook said: "We will stop them.

"I would like to think we would police it quite reasonably, but at the end of the day we will use whatever means is necessary or appropriate reasonable force if necessary.

"I am not saying it's impossible (to break through the cordon), but obviously the police are there to make sure it doesn't happen.

"Hopefully we will not get to the stage where we have to chase them, because we would have stopped them. This is all about preventing serious injuries and saving lives."

However, police will not use batons or CS spray to enforce the road closure.

An ambulance crew and 10 first aiders will be on duty near Magdalen Bridge.

Last May Morning in Oxford, which is not an official public event, 12,500 revellers turned up to hear Magdalen College Choir performing the Hymnus Eucharisticus from the top of the college's tower.

The bridge was closed on May Morning between 1998 and 2001, but last year a Sunday 8,500 people stood on the bridge and 12 jumpers were taken to hospital, some with broken legs, ankles and ribs.

The River Cherwell is currently only a foot deep in places and riddled with debris such as broken glass, rocks and supermarket trolleys. Paramedics also think there is a chance jumpers with open wounds could catch the deadly Weil's Disease an infection carried in rats' urine, contaminating ponds and rivers.

Adrian Fellows, emergency planning manager of Oxfordshire Ambulance NHS Trust, said: "Last year people were jumping on to injured people who were screaming 'don't jump' but they still did.

"From the bridge you could hear the snap of bones it's unimaginable."