The statistics surrounding the Martell Grand National include a total of £100 million bet by over 10 million people and an worldwide armchair audience of 650 million. Throw in a colossal security effort to combat the twin threats of lunatics and disease and the build up more than justifies the Aintree highlight's status as the world's most famous steeplechase. And yet the most important factor of all today is what falls from the sky for nothing.

Rain started to lash on Liverpool on Thursday morning, briefly stopped for a breath yesterday but it is forecast to start tipping down again today. The result is sceptics are betting there will be fewer finishers today than the six that struggled home behind both Earth Summit (1998) and Minnehoma (1994).

Another result is an ante-post market that has been turned on its head as punters have plunged on horses that have a proven track record on very soft ground. Mudlarks such as Moral Support and Hollybank Buck have been receiving the sort of interest they might not normally get. But the most popular horse for money has been Edmond, who is set to challenge last year's first two, Papillon and Mely Moss, for favouritism, having been more than 20 to 1 on Wednesday.

Ted and Ruby Walsh have been busy trying to get Papillon settled back into Aintree after the horse's late flight to Speke Airport yesterday afternoon but admit they are worried the rain will impede their star's chances of becoming the first since Red Rum (1973-74) to win back-to-back Nationals.

"Papillon has won on bad ground but he has also run some stinkers, and I'd have been a lot happier if the rain had stayed away. He just can't travel as well on soft ground but it was fast last year and he loved it," Ruby Walsh said yesterday. The sentiments were shared by his father who did, however, admit to satisfaction with the horse's fitness, and Papillon's proven ability around the track as well as his class mean he is a frontrank contender again.

Imagine, however, how the rain has been greeted by one punter who stands to win £500,000 from a £100 each-way bet if Mely Moss wins today. The Coral customer had a treble on Nimello at 20 to 1 to win the Lincoln, Ibal at 16 to 1 to win the Imperial Cup. He has 14 to 1 about Mely Moss, but the horse was on the drift yesterday due to doubts about him on the going.

The two other Irish contenders are Hollybank Buck, who was the best backed outsider with Ladbrokes yesterday, and Merry People, who has squeezed into the race as first reserve. The ex-Michael Hourigan-trained Inis Cara has been transferred to Venetia Williams only this week and his proven ability on heavy ground gives him a squeak, a fact that some shrewdies pounced on yesterday.

Other horses who fall into the squeak category look to be Village King, who travelled brilliantly to the 20th last year, and Spanish Main, but the circumstances now look to dictate the main bet should be a horse who has a light weight, a strong jockey and an insatiable appetite for muck and hardship. Just like last year when Papillon was backed to the exclusion of everything else, the punters look to have got it absolutely right with Edmond.

The former Welsh National winner seems to have limitless stamina, is a solid jumper and by reputation has to have dig in the surface just to walk. The P for pulled up next to his name is hardly encouraging but he will don blinkers for today's race and is one of the few who will relish the conditions.

Richard Johnson has yet to finish the National in four rides, but he did win the John Hughes over the big fences yesterday and has a proven big-race record, with a Gold Cup on Looks Like Trouble already under his belt. He can complete steeplechasing's ultimate double on Edmond. The best each-way alternative could be Village King, with Hollybank Buck a strong possibility for a place.

The main supporting race is the Martell Aintree Hurdle, which can see Hors La Loi III get compensation for being outpointed by Mister Morose in this event last year. The Paul Green-owned runner bounced back to something like his best form at Wincanton last time and this time around isn't coming here on the back of a hard race in the Champion Hurdle.