It is absolutely vital to get all of the facts about what has happened

RSPCA spokeswoman

On Thursday, Strong Promise, Rossell Island and Architect all suffered fatal falls while Lake Kariba had a heart attack at the end of a race.

A spokesman for Kent-based Animal Aid said an inquiry should be launched with a view to prosecuting organisers of the event under the 1911 Protection of Animals Act.

"Given the punishing nature of the Grand National course and the record of horse fatalities, Animal Aid believes there is a prima facie case for prosecution," the spokesman said.

'Slight mistake'

But the trainer of Toni's Tip, Ferdy Murphy said: "It's just one of those things and could have happened anywhere.

"He made a slight mistake and went to save himself. He was a really good jumper who must have fiddled two or three hundred fences in his time."

An Aintree spokesman said there would be a post mortem examination at a nearby Vetinary Hospital.

Go slow instruction

Meanwhile an urgent meeting has been held between the RSPCA, the Jockey Club and Aintree management to try to prevent further deaths.

An RSPCA spokeswoman said the course would be fully watered overnight in an effort to slow the going.

Jockeys will be told to reduce their speed coming up to the first fence and the rail will be moved so the jump hits fresh ground, she added.

RSPCA inspectors will also be positioned at each fence on Saturday.

Asked about the call for a prosecution of Aintree's organisers, the spokeswoman added: "It is absolutely vital to get all of the facts about what has happened.

"We will have to wait to see the post mortem results, which will indicate the cause of death in each case."

Animal rights activists are calling for a ban on the race and are urging people not to place bets.

But a spokesman for William Hill said the level of betting was very high this year, due in part, to bets being placed on the internet.