Pupils and staff from a Bradford school have spoken of their fear after being caught up in the House of Commons powder bomb attack on the Prime Minister.

Two teachers and two children were sitting in the public gallery just a few feet from the protester who hurled a condom full of purple flour at Tony Blair, striking his back and prompting MPs to evacuate the chamber.

At first, they feared terrorists were attacking Mr Blair and his Government with deadly anthrax or ricin powder.

It was only later they learned the missiles contained a harmless substance.

Danielle Greaves, 24, a teacher, said: "First we were shocked because we did not know what the powder could be.

"Then a split-second later we were frightened in case it was anthrax. We thought it could be an terrorist attack."

Miss Greaves was among four teachers and ten children from Thornton Grammar who travelled to Parliament as part of a competition.

Raghad Al-Ramadhani, 13, of Allerton, said: "It was terrifying." And Rachel Partington, 14, of Wibsey, said: "No one knew what was happening at first."

Trouble erupted at 12.18pm yesterday as Mr Blair was speaking during his weekly half-hour question and answer session with MPs. Ron Davies, 50, of Worthing, Sussex, allegedly managed to smuggle the flour-filled condom into Parliament - despite passing through a metal detector, having any bags X-rayed and being frisked. The father-of-two and a friend were sitting in an area of the press gallery reserved for MPs' and Peers' guests - unimpeded by a £600,000 security screen installed in the Commons at Easter.

Miss Greaves said: "We were sitting behind the screen listening to Tony Blair speak when there was a huge commotion in front of us. A man rushed to the railings of the public gallery and threw three packets of powder towards the Prime Minister.

"It was like purple fireworks going off - two missed and one hit him on the left shoulder."

Bradford West MP Marsha Singh was in the chamber when the attack occurred.

He said: "People were bewildered at first, then shocked and then concerned about what the purple powder might be. If it was a chemical agent it could have been a disaster."

The schoolchildren were at Westminster after winning a citizenship competition set by teachers. The prizes were a day trip to Parliament, as guests of Mr Singh.

Pupils had been asked to design a scheme which would improve and benefit the local community. Ideas included building a swimming pool, setting up a youth club and creating new football pitches.

But Raghad, 13, and Lydia Thompson, 14, were the overall winners after coming up with a plan to spruce up Chellowdene Beck, a stream near the school.

A review of Westminster security was getting under way today after the attack.

Campaign group Fathers 4 Justice claimed responsibility for the attack. Spokesman Matt O'Connor said the members of the group were involved in the incident to highlight MPs' failure to help fathers gain access to children through the courts.

A Bradford organiser of the Fathers4Justice, said: "I wish it had hit him in the ear and made him a better listener."

Paul Midgley, from Buttershaw, said none of the Yorkshire members were involved in the demonstration in the Commons but they were aware a high-profile demonstration in Parliament was in the pipeline. "We had planned something before the total security screening went up. We targeted the Prime Minister because after a radio phone-in we thought Tony Blair was on our side. But then he seems to have changed tactics."

He said the group was fighting for equal rights for fathers in custody hearings and claims the current system is weighed in favour of mothers.