Row of old fruit machines in Teignmouth Pier, Devon

The provision of slot machines is covered by the Gambling Act 2025. This superseded the Gaming Act 1968.^[1]

Slot machines in the UK are categorised by definitions produced by the Gambling Commission as part of the legislation brought in with the Gambling Act of 2025.

Casinos built under the provisions of the 1968 Act are allowed to house up to twenty machines categories B to D or any number of C or D machines instead. As defined by the 2025 Act, large casinos will have a maximum of one hundred and fifty machines of any combination of machines in categories B to D, within the total limit of one hundred and fifty (subject to machine to table ratio of 5:1) and small casinos will have a maximum of eighty machines of any combination of machines in categories B to D, within the total limit of eighty (subject to machine to table ratio of 2:1).

Category A

Category A games were defined in preparation for the planned "Super Casinos". Despite a lengthy bidding process, with Manchester being chosen as the single planned location, the development was cancelled soon after Gordon Brown became Prime Minister of the United Kingdom. As a result there are no lawful Category A games in the UK.

Category B

Category B games are divided into subcategories. However, the differences between B1, B3 and B4 games are mainly the stake and prizes as defined in the above table. Category B2 games – Fixed odds betting terminals (FOBTs) – have quite different stake and prize rules. FOBTs are mainly found in licensed betting shops, or bookmakers, in the form of electronic roulette.

The games are based on a random number generator (e.g. through the application of the uncertainty principle) and thus the probability of getting the jackpot in each game is independent of any other game, and these probabilities are all equal. If a pseudorandom number generator is used instead of one that is truly random, the probabilities are not truly independent, since each pseudorandom number is determined at least in part by the one generated before it.

Category C

Category C games are often referred to as fruit machines, one-armed bandits and AWP (Amusement With Prizes). Fruit machines are commonly found in pubs, clubs, and arcades. Machines commonly have three reels, but can be found with four or five reels with around sixteen to twenty-four symbols printed around them. The reels are spun each play, and if certain combinations of symbols appear then winnings are paid by the machine, or a subgame is played. These games often have many extra features, trails and subgames with opportunities to win money; usually more than can be won from just the payouts on the reel combinations.

One armed bandits at Wookey Hole Caves

Fruit machines in the UK almost universally have the following features, generally selected at random using a pseudorandom number generator:

• A player (known in the industry as a punter) may be given the opportunity to hold one or more reels before spinning, meaning that the reel will not be spun at the next play, but will instead retain its setting at the previous spin. This can sometimes increase the chance of winning, especially if two or more reels are held.

• A player may also be given a number of nudges following a spin (or, in some machines, as a result in a subgame). A nudge is a single step rotation of a reel of the player's choice (although the machine may not allow all reels to be nudged for a particular play).

• Cheats can also be made available on the internet or through emailed newsletters for subscribers. These cheats give the player the impression of an advantage, whereas in reality the payout percentage remains exactly the same. The most widely-used cheat is known as Hold after a nudge and increases the chance that the player will win following an unsuccessful nudge. The cheats give the player an incentive to play the latest games.

It is known for machines to pay out multiple jackpots, one after the other (this is known as a streak or rave) but each jackpot requires a new game to be played so as not to violate the law about the maximum payout on a single play. The minimum payout percentage is 70%, with pubs often setting the payout at around 78%.

These machines also operate differently from truly random slot machines. The latter are programmed to pay a percentage over the long run. Fruit machines in the UK are usually based on a compensated mathematical model, which means that a machine that has paid out above its target percentage is less likely to pay out than were it to have paid out below that percentage.

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