Introduction
The "rule of the loaded gun" is a colloquial phrase used to describe a principle within the law of evidence concerning the admissibility of a defendant's bad character or propensity to commit certain crimes. This essay will discuss the origin and meaning of this rule as it developed at common law, before explaining how the legal position has been fundamentally altered by the introduction of the statutory framework in the Criminal Justice Act 2003 (CJA 2003). It will be argued that while the CJA 2003 has replaced the common law, the underlying idea that specific propensity can be relevant evidence has been retained, albeit within a more structured and regulated system.
The Common Law "Rule of the Loaded Gun"
The phrase originates from the judgment of Lord Sumner in the House of Lords case of Thompson v The King [1918] AC 221. In this case, the defendant was charged with gross indecency with two boys. The identity of the perpetrator was the central issue. Evidence was admitted that, upon his arrest, the defendant was found to be in possession of powder puffs, and that indecent photographs of boys were discovered at his lodgings. The House of Lords held that this evidence was admissible. It did not merely show that the defendant was of bad character in a general sense; rather, it demonstrated a specific and unusual propensity that was relevant to identifying him as the person who had committed the particular crimes alleged.
Lord Sumner explained the distinction with a powerful analogy. He stated that simply proving a man has burglar's tools on him days after a burglary does not prove he committed that specific burglary. However, he continued by way of illustration:
> "The possession of a loaded gun is a very different thing from the possession of a box of matches, and, if a man is charged with setting fire to a haystack, the fact that he was found near by with a box of matches in his pocket is a fact on which the jury would not be allowed to speculate, but if he were a person who was proved to have a disposition to commit arson, the fact that he had a box of matches upon him would be a very different thing." (Viscount Haldane in Thompson v The King [1918] AC 221, at p. 226, summarising the argument)
The principle, therefore, was that while evidence of general bad character was typically excluded as being unfairly prejudicial, evidence showing a defendant had a "special and peculiar propensity" for committing the specific type of crime charged could be admitted if its probative value was sufficiently high (Keane and McKeown, 2022). This became part of the 'similar fact evidence' doctrine, which was later rationalised in cases like DPP v Boardman [1975] AC 421, where the court held such evidence could be admitted if its probative value outweighed its prejudicial effect, often where there was a 'striking similarity' between the past conduct and the present charge.
The Modern Position under the Criminal Justice Act 2003
The common law rules on bad character evidence, including the 'similar fact' doctrine and the "rule of the loaded gun", were complex and often criticised for being uncertain. In response, Parliament enacted the Criminal Justice Act 2003, which abolished the common law rules (s.99 CJA 2003) and replaced them with a new statutory scheme for the admissibility of a defendant’s bad character evidence (ss.98-113 CJA 2003).
Under the CJA 2003, "bad character" is broadly defined as evidence of, or a disposition towards, misconduct (s.98). Such evidence is not admissible unless it passes through one of the seven "gateways" set out in section 101(1). The gateway most relevant to the old "rule of the loaded gun" is s.101(1)(d), which permits the admission of bad character evidence if "it is relevant to an important matter in issue between the defendant and the prosecution".
Section 103(1) clarifies that this includes the issue of whether the defendant has a "propensity to commit offences of the kind with which he is charged". This directly reflects the principle from Thompson. However, unlike the common law, the CJA 2003 provides statutory safeguards. The court must not admit evidence under this gateway if, on the prosecution’s application, its admission would have such an adverse effect on the fairness of the proceedings that it ought not to be admitted (s.101(3)). This requires the judge to explicitly balance the probative value of the propensity evidence against its potential for unfair prejudice, continuing a key theme from the common law but within a statutory checklist.
Conclusion
In conclusion, the "rule of the loaded gun" was a memorable judicial attempt to explain why evidence of a specific, relevant propensity could be admissible when general evidence of bad character was not. It was a key part of the common law's approach to similar fact evidence. However, this area of law is now governed exclusively by the Criminal Justice Act 2003. The Act has replaced the old common law rules with a more transparent and structured regime. While the language of "loaded guns" is no longer used, the underlying concept that a defendant's propensity can be a highly relevant piece of evidence persists through the gateways to admissibility in the CJA 2003, particularly the gateway concerning important matters in issue. The modern law, therefore, continues the principle but places it within a clear statutory framework designed to better regulate its use and protect the fairness of the trial.
References
DPP v Boardman [1975] AC 421
Keane, A. and McKeown, P. (2022) The Modern Law of Evidence. 14th edn. Oxford University Press.
Thompson v The King [1918] AC 221
Criminal Justice Act 2003
