British horse racing stands to benefit by more than $A40 million from Mon Mome's upset Grand National win.

The 100-1 shot left punters reeling at Aintree on Saturday, but the sport will cash in from an industry funding system that requires bookmakers to return 10 per cent of their gross profits.

British bagmen were understandably tight-lipped about their Grand National result on Sunday.

Bookmakers who had been quick to specify losses after favourite Comply Or Die won last year's edition were coy about this year's figures.

Representatives for industry heavyweights, Ladbrokes and Coral, restricted themselves to admissions Mon Mome's win had been worth "tens of millions" to them.

Estimates of an industry-wide 200 million pound haul would mean a STG20 million ($A41.44 million) payout to horse racing from the gruelling 7200m steeplechase.

Racehorse Owners' Association secretary, Michael Harris, explained to Racing Post why a disaster for punters meant a windfall for the sport.

"A 100-1 winner is very good news for racing," he said. "It should be a windfall for racing."

Trainer Venetia Williams, only the second woman to prepare a Grand National winner in the race's 170-year history, is still being feted by owners and friends.

Supporters organised a fly-past by a twin-engined aircraft with a giant Union Jack painted on its wings on Sunday.

Williams had just returned to her Hertfordshire stables from a big night in the local Lough Pool pub in time to witness the victory salute.

She said her stable star, a French-bred nine-year-old, would now be spelled.