Cambridge University students earned the wrath of the public after a bank holiday bender involving wielding a pig’s head on a stake, drunken students vomiting and urinating in bushes and daubing themselves in war paint to take part in organised fights.

About 1000 Cambridge students gathered for Caesarian Sunday, a riotous party in a city centre public park to mark the beginning of the summer term.

But visitors to Jesus Green, including many with children, who went to soak up the warm weather, were subjected to views of Cambridge students fighting, stripping off, vomiting and urinating in bushes and flower beds.

Many of those taking part in the bizarre initiation ceremonies were members of drinking societies of the various Cambridge University colleges.

Girls were seen drinking port through condoms and others downed pints while wearing stinking necklaces of kippers.

It comes as an investigation was launched into the burning of a Union flag in a courtyard of Cambridge University’s King’s College during the royal wedding.

However, the centrepiece of Sunday’s riotous event was an organised fight between the drinking societies of Cambridge University’s Jesus College and Girton, known respectively as the Caesarians and the Green Giants.

Several students were left bloodied and bruised by the combat as colleagues cheered them on.

Although police spoke to revellers, no arrests were made.

Janet Banner, 34, who was picnicking in the park with her partner and two teenage children, said: “There was lots of rubbish flying across Jesus Green, guys urinating in front of us, bad language, and people carrying a pig’s head on a stick.

“The police were called at one point but didn’t do anything. I am sure if they weren’t students they wouldn’t get away with it.

“Surely Cambridge University students should not be behaving like that.”

A mother-of-two, who asked not to be named, said: “I was with my son who is only five and didn’t understand what was going on. He was terrified and we had to leave.

“It is disgusting what was allowed to go on. It may be a public park but that doesn’t mean you can do what you want.”

Another visitor said: “The students were running around semi-naked, vomiting and singing rowdy drinking songs.

“It’s not something I’d expect to see in the centre of Cambridge on a Sunday afternoon and I’m furious my kids were exposed to it. Some of the students were totally out of control.”

Caesarian Sunday takes place on the first bank holiday of the summer term and is regarded as the last opportunity to let off steam before the gruelling summer term, which concludes with end-of-year exams.

It is said to have started when a member of the Green Giants stole a bottle of Pimm’s from a Caesarian. The bottle was then thrown at the Caesarian in a challenge to fight.

Now, every year, the president of Girton’s drinking society downs a bottle of Pimm’s and invites the Jesus drinking society to fight.

By about 3pm on Sunday, more than 20 male Cambridge students wearing ‘war paint’ on their faces fought each other.

One team, wearing makeshift togas, held aloft a pig’s head on a stake as they marched in to battle.

Afterwards, some students jumped into the nearby River Cam in their underwear or staggered into nightclubs.

A student, who declined to be named, said: “The fighting was pretty vicious this year. A lot of the stuff that goes on is really quite shocking, especially as it’s in a public place, but most of the students are so drunk they just don’ t care.

“Many of them started drinking at breakfast or even the night before and have just carried on drinking all day.

“For the drinking societies it is one of the biggest events in their calendar and some graduates even come back especially for the occasion.

“Many of the students think they work hard, so deserve to drink and party.”

Meanwhile, senior college officers and student leaders have held a meeting to try to identify those responsible for the flag burning on Friday.

During the early stages of the service the large Union flag which was the centrepiece of the college bar’s royal wedding decorations, was removed and burnt in Chetwynd Court.

Some students disclosed that an antimonarchy protest had been held at King’s at the time of Prince William and Catherine Middleton’s wedding.  “There’s a core group of about 20 or 30 republicans here that do protests and that kind of thing,” said Matt Merrick, the college entertainments officer who organised the event in the bar.

“It’s embarrassing for a college and university that on the day the heir to the throne becomes the Duke of Cambridge we have students burning the national flag. It’s a small minority who have done this.”