Bookmakers were predicting on Thursday night that reigning champion Kauto Star will start the hot favourite for the Gold Cup, despite fears that steady rain would turn conditions in favour of his stablemate and big rival Denman.

Around £300million will be bet on a day when a sell-out 65,000 crowd will flood into Cheltenham.

With bookies estimating yesterday's Cheltenham bets totalled £250m and Tuesday's figure was put at £100m, the three days of the meeting will have attracted a staggering £650m betting bonanza.

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The clash between stablemates Denman and Kauto Star on an extended nine-race card is expected to push turnover beyond the record £255m bet on Grand National day last year.

Betting exchange Betfair predict that trading on the Gold Cup, run on ground unraced on since last year's Festival, will breach £10m on a race for the first time on their exchange.

The going remains good to soft, good in places. Gold Cup sponsors totesport quote Kauto Star as evens favourite to retain his crownwhile Denman is a 13-8 shot.

Racing has been waiting for the clash between the two geldings, who live only feet apart at trainer Paul Nicholls' Somerset stable, since last year's Festival when Kauto Star won his first Gold Cup and Denman, who has never been beaten in eight races over fences, graduated from the novice ranks with victory in the Sun Alliance Chase.

Their clash is being billed as the biggest steeplechasing dual since the 1964 Gold Cup between Arkle and Mill House.

Between £30m-£40m will be bet on the Gold Cup alone.

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