Parents are worried about the alleged effects of phone masts

A team of contractors were confronted by the man as they arrived to start work on the equipment opposite St Wilfrid's Primary School in Newton Heath, Manchester.

The proposals have sparked opposition among parents who are worried about the alleged health risks.

They recently organised a picket outside the school with some parents taking their children out of classes to join in.

The organisers of the protest have condemned the assault, but said that they will fight to stop the plans.

Pamela Flynn, a shop owner and grandmother to four pupils at the school, said: "We don't want acts of violence, but we will take legal steps."

I am shocked at the violence and the experience was obviously very frightening O2 spokeswoman

The mobile phone company O2 hired the contractors to start work on the mast at Newton Heath Cricket Club.

The firm was granted planning permission for the mast after an appeal.

'Very frightening'

A spokeswoman for O2 said: "I have never come across anything like this.

"I am shocked at the violence and the experience was obviously very frightening."

A spokeswoman for Greater Manchester Police said the incident was under investigation.

The government has said a recent study showed that emissions from mobile masts in the UK are well within international guidelines.