POLICE are planning a massive security operation for this evening's Martell Grand National, details of which are being kept secret.

Privately, organisers are concerned at the possibility of a repeated bomb threat. One senior police source said: "No matter how many security precautions we take you can never be completely confident that a bomb alert is a hoax."

Racecourse officials and police considered their options overnight before finally agreeing to put a contingency plan into action. Only the Grand National will be staged, entry will be free to most areas.

Security will be stepped up even further and no cars will be admitted on to the course. "It's part of our national heritage and we wish to run this race," said clerk of the course Charles Barnett.