This could be the day when the bookmakers face the biggest pay out in history.

Shutthefrontdoor could go to post as the shortest-priced favourite for the Crabbie's Grand National in over 40 years for the startlingly simple reason that he has been chosen by AP McCoy as his last ride in the race before retirement.

There will be upwards of £150 million wagered on this year's National with a win for Shutthefrontdoor seeing bookmakers across the country facing a pay out of more than £30 million.

Shutthefrontdoor's price has dropped from 25-1 in February to 7-1 and could shrivel even further today as the once-a-year punters jump on the McCoy bandwagon. However, history shows that such monumental public gambles can go badly wrong.

The shortest-priced winner of the race, Poethlyn in 1919, was sent off at 11-4 having already won a wartime version of the National run at Gatwick, the previous year. However, those punters who lumped on Golden Miller in 1935 did not collect.

The star of his generation, Golden Miller won the Cheltenham Gold Cup five times but his love affair with Aintree was very much a one-race stand. Having fallen at the Canal Turn on the second circuit in the 1933 race, Golden Miller won the following year in a record time and broke another record in 1935 when he was sent off as the 2-1 favourite, the shortest price in the race's history. However, the rot had already set in.

Golden Miller's flat style of jumping may have been suited to park courses but not to the drop fences of Aintree and his dislike was made plain in this race where he jumped the tenth fence crooked and fired Gerry Wilson out of the saddle. The punters still backed him when he ran at Aintree again but Golden Miller failed to show in two further attempts in the National, falling in 1936 and refusing in 1937.

By contrast Freddie, trained in the Borders by his owner Reg Tweedie, attacked the big fences with a relish. Freddie started the 1965 National as the 7-2 favourite, only to be beaten just three-quarters of a length by Jay Trump and was back 12 months later as the 11-4 favourite the following year but was second again, this time being beaten 20 lengths by Anglo.

Even the mighty Red Rum let the punters down when they had the most faith. Having won the race in 1973 and '74 the money poured in for Red Rum who was just a 7-2 chance to make it three in a row, only to finish second to L'Escargot.

Over the last 30 years only five favourites or joint-favourites - Rough Quest in 1996, Earth Summit in 1998 Hedgehunter in 2005, Comply Or Die in 2008 and Don't Push It in 2010 - have won but bookmakers are bracing themselves for the sort of battering they last took when Frankie Dettori won all seven races at Ascot in 1996. The tills stopped rattling at £40million then.

David Williams, of Ladbrokes, said: "A win for McCoy is our nightmare scenario. Shutthefrontdoor could easily be the best backed horse we've ever known in the Grand National. We're scared even to think about it.

"More often than not Aintree throws up a host of stories but this year there's only show in town. The entire race revolves around one man and one horse.

"We reckon it will cost the industry £30 million if McCoy wins but that could be conservative. If the nationwide gamble unfolds the liabilities could go through the roof. The total cost could be disastrous."