ZARA Phillips this week launched a fund-raising campaign aimed at giving 20,000 primary school children a taste of horse riding for the first time. The Princess Royal’s daughter, a keen rider, posed on “Trigger” - a mechanical horse that will allo thousands of youngsters a chance to try riding. Miss Phillips was joined at the launch in London’s Hyde Park by children from Holy Trinity primary in Sloane Square, London, who received free instruction at a riding centre in the park.