P665 CJEFAX 1 665 Tue 31 Mar 21:14/42       STRICT SECURJTZ FOR NATIONAL All of the estimated 60,000 racegoers attending Saturday's Martell Grand National will bj subject to strict security checks. Contingency plans have also been drawn up to deal with demonstrations by "extremist groups" and hoax callers. Security measures will bj similar to those at airports, with racegoers urged to arrive at the course early. Supjtintendant Ray Rjvill-Johnson said: "Wj are determined to ensure everyone can enjoy this jvjnt in safety." WEN RIDER TONY McCOY'S BIOGRAPHY 668 Daily Quiz 685 BHB 691 Race News 661 Dobbin Dorans King/Time Universal