It's a whole new ball game, growing bigger by the minute. And on the day when a Texan billionaire takes centre stage at Lord's to announce details of the most lucrative match in the history of cricket, the biggest question is whether Twenty20 will not only rule in years to come but also make every other form of the sport obsolete.

Sir Allen Stanford has already decided that Test cricket is "boring". Difficult for many to credit, certainly, yet it is a safe bet his view will be shared by a least some of the tens of thousands of spectators who pack out county grounds around the country this evening to welcome back what is correctly, though belatedly, being billed as the "original" Twenty20 Cup.

Five years ago, England Cricket Board officials thought they had a good idea. Most others, including a lot of players and coaches, were far from certain. But no one guessed a game of 20 overs a side - albeit one with music, sideshows and non-stop action - would prove to be a blockbusting success.

Sir Allen's first £10million match, between England and his West Indies All Stars XI, will be played in Antigua in November, six months after the inaugural, multi-million pound Indian Premier League changed the sport's landscape for ever.

And a few weeks before the Caribbean bash, an English county could be lining up against an Australian state, South African province or Indian franchise for a Champions League winners' cheque of £2.5m; provided the new eight-team tournament is not ruined by rows over rebel players.

Twenty20 is awash with prize money. Well, all apart from the "original" competition, which will pay out a relatively piffling £42,000 to the team crowned Cup kings at Southampton's Rose Bowl on 26 July. The number of games keeps increasing (90 during this year's group stage compared to 45 in 2003) but the pay-outs don't change much. Yet.

Within a few weeks the ECB will announce plans for a beefed- up Twenty20 Cup from 2010, possibly buoyed by more Stanford cash and almost certainly including extra overseas players to capture the interest of a wider television audience.

Where will that leave Test cricket, even in this country with its proud record for attracting big crowds to five-day cricket?

Kent captain and former England batsman Rob Key is not certain, suggesting the longer game could be under threat from Twenty20 come the 2020s.

"Certainly not in my time as a cricketer, and certainly not for the next 10 or 15 years, but a long way down the line there's every chance," said Key, whose county won last year's domestic competition. "The game has to evolve." As for the four-day game, Key said: "A championship game makes Kent, on a good week, £5,000. But on a Twenty20 game in three hours they might take £50,000. So in the long term, who knows?

"I think it would be sad if Test cricket wasn't around. For me, four and five-day cricket is the true test.

"When I retire I'll look back at the hundreds I scored in four-day games with a lot more pride than the runs I got in Twenty20. The true sense of achievement for me, and I think most players, comes from the longer form.

"Whether that's the same 10 or 15 years down the line, I would say it probably isn't going to be. Most kids now want to be learning how to hit the ball a long way."

However, the 29-year-old Kent player also loves being let off the leash.

"When the competition started those of us at Kent didn't think it would still be around by now," he said. "But it's getting bigger and bigger, and it's great fun to play in."

And to watch. "We will have three or four sell-outs from our five home matches," said Surrey chief executive Paul Sheldon. "Our players think Twenty20 is more exciting than ever and, clearly, so do spectators."