Deputy Prime Minister Mr John Prescott was last night involved in a violent confrontation with a demonstrator as he attended a Labour Party rally.
Mr Prescott was hit by eggs and jostled by an angry crowd as he arrived at a theatre in Rhyl, north Wales.
Television pictures showed Mr Prescott being pelted with an egg as he walked towards the theatre.
He was then seen turning to his left and apparently punching a man on the chin. The man then lunged towards Mr Prescott, trapping him against a wall.
A Labour Party spokesman said Mr Prescott had defended himself against attack "as anybody would in the circumstances".
But the local Conservative parliamentary candidate, Mr Brendan Murphy, called on Mr Prescott to resign.
Meanwhile, a senior Labour Party source said last night: "We have got serious, serious legal advice surrounding the circumstances of this event and we are confident our statement is right."
A man was arrested following the incident and was being questioned by north Wales Police.
Mr Prescott was heckled from the minute he stepped off the Prescott Express battle bus.
At least two eggs were thrown at him as he walked towards the Little Theatre in the seaside town. He was trapped against a narrow wall as party supporters freed him from the protesters.
With egg splattered on his jacket, Mr Prescott was led safely into the theatre by police.
A Labour Party spokesman said: "John Prescott was attacked by a protester as he made his way into a campaign event in Rhyl.
"He defended himself from the attack as anybody would in the circumstances."
More than 30 protesters, many with placards, earlier congregated outside the theatre.
One poster bore the slogan "Average farming wage in Wales £75 a week" while others declared support for hunting.
A convoy of demonstrators led by last year's fuel protest leader, Mr Brynle Williams, later drove past the Rhyl Theatre where the Labour Party rally was taking place.
The crowds outside the theatre grew later as fuel protesters, including Mr Williams, joined the demonstration.
Mr Williams, who arrived after the melee, said he did not condone the violence, which broke out in front of the hall.
A witness Mr Ron Ingram, a farm labourer, claimed he saw Mr Prescott lash out when he was hit by an egg.
"Somebody threw an egg and Prescott just turned around and thumped them. I saw it. We were just protesting. The egg hit him and he hit out."
Mr Murphy, Conservative candidate for the Vale of Clwyd, called on Mr Prescott to resign.
"He's just got to resign and get it over with. What sort of role model is he for young people. We don't want that kind of role model in Rhyl."