Fathers' rights protester Ron Davis has been convicted of disorderly behaviour for helping carry out a purple flour bomb attack on Tony Blair.

Davis, 48, was given a two-year conditional discharge following a two-day trial at Bow Street Magistrates Court in London.

The father, of Vale Avenue, Findon, near Worthing, brought Prime Minister's Questions to a halt during the protest on May 19, sparking fears the House of Commons was under biological attack.

He helped organise the stunt during which Mr Blair was pelted with condoms filled with purple flour and glitter. The chamber was evacuated and police, thinking it was an act of terrorism, were sent to the building in protective suits and gas masks.

Deputy Senior District Judge Daphne Wickham told Davis his actions caused "appalling levels of anxiety".

During the one-and-a-half day trial, the court heard Davis, a member of campaign group Fathers4Justice, had gone to the chamber with fellow group member Guy Harrison, who had won VIP tickets in a raffle.

Fifteen minutes into Prime Minister's Questions Davis got up, blocked the corridor in the public gallery and unfurled a banner which read "Flower Power for Dads".

It enabled Harrison, 36, from Ashurst, near Steyning, to hurl three condoms into the chamber, hitting Mr Blair in the back.

Sentencing Davis yesterday to a two-year conditional discharge and ordering him to pay £500 costs, Judge Wickham said members of the public in the galleries had told of their fear when they did not know what was happening.

She said: "This is a country which is and remains in a high state of tension in relation to a terrorist attack. To put those people through that was unforgivable, even if it was for half an hour."

Giving evidence yesterday, Davis, who had pleaded not guilty, told the court of his anguish in being prevented from seeing his children.

He said he had not seen his 13-year-old daughter for six years.

He said he had spoken to his 11-year-old son for about a minute at the end of his road in October last year.

The court heard his health had deteriorated while he fought through the family courts to see his children.

This year alone, he said, he had been to court 20 times.

The 48-year-old said he had lost his home and liquidated his electrical wholesale business to pay the £26,000 legal fees racked up over the years.

However, when he took his wife to court for ignoring a contact order, the order was revoked. He said: "I could barely hold myself together. You think an awful lot about your children and it's difficult to keep going. The injustice eats into you."

The court heard Davis decided to go to the House of Commons with Mr Harrison a few days after the contact order was revoked. He said: "I was absolutely devastated."

Throughout the trial Davis insisted the stunt was a peaceful protest to highlight the plight of fathers denied access to their children and not intended to cause distress. He said there was no plan to throw the condoms into the chamber and he was surprised when Mr Harrison threw them.

However, Judge Wickham said Davis's actions, particularly in causing distress to children who were present, discredited his cause.

On Monday, a 17-year-old schoolgirl told the court she had thought the protest was a terrorist attack and had been "very scared".

Speaking outside the court yesterday, Davis said: "I think it's a real shame there is a necessity to find someone guilty for what was a peaceful demonstration.

"The judge gave a guilty verdict but I think the punishment reflected people's truer feelings. This will absolutely not put me off. I will continue campaigning for better contact rights for children and fathers.

"I didn't set out to distress anyone intentionally. Sometimes you have to challenge bad laws in order to get them changed."

Harrison, who pleaded guilty to using threatening words or behaviour, was fined £600 in May.