In the studio stands a 15-foot (4.6 m) hourglass filled with tokens that represent an initial prize pot of £50,000. At the start of the game, the two contestants each decide which role they will play. One is the "Game Player" and must play through five rounds; the other is the "Time Keeper," responsible for deciding how much time the Game Player will have to complete each round before the prize pot begins to decrease. In addition, the Time Keeper chooses the category for each round. Seven vague categories are presented at the start of the game, such as Animal Lover, Couch Potato, Film/History Buff, Trivia Junkie, and Wordsmith; categories are removed from the list as they are used. The Time Keeper is given a total of five minutes to allot over the five rounds, and is advised to give more time to categories that may pose a challenge to the Game Player.
In each round, the Game Player must give five correct answers. Once the Time Keeper chooses a category, an example of the specific game to be played (27 in all during the first series) is shown to both contestants, after which the Time Keeper sets the time limit. Frequently, the Game Player must respond in an unconventional manner, such as spelling the answer backwards or by using the numbers on a touch-tone telephone keypad. He/she may pass as often as desired, but as there is a limited bank of questions for each round, passing too often will eventually cause the questions to cycle. The Game Player may guess on any question as many times as desired, but can move on to a new one only by giving the correct answer or passing. Answers to any passed questions are revealed once the round is complete.
If the Game Player reaches the final 10 seconds of the time allotted by the Time Keeper, the hourglass begins to flip. Once time runs out, the tokens start to drain into the lower section and the prize pot begins to decrease accordingly, at a steady rate of £625 every three seconds (£12,500 per minute). The round continues until either the Game Player gives a fifth correct answer or the hourglass has completely emptied. In the former case, the draining stops as soon as the answer is given; in the latter case, the Game Player "crashes out," the game ends, and the contestants leave with no money. If the Game Player completes the round within the allotted time, the prize pot remains intact but any extra time remaining on the clock is lost.
The two contestants may not confer at any time once they have chosen their roles. Once during the game, the Time Keeper may press an Emergency Stop button to halt a round if the Game Player is struggling badly. The current category is thrown out, and the Game Player plays a makeup round (the "Emergency Game") using a category randomly chosen from the ones still in play. The Game Player has the same time limit for the Emergency Game as he/she had for the one stopped by the Time Keeper, but this time is not deducted from the team's overall five-minute allotment. Money drained during the stopped game is not replaced in the hourglass.
At the end of each round, the drained money is counted and removed from the hourglass, and the remainder is kept in play for the next round.