A moped rider is stopped at an intersection. Behind him is a van.

Another moped with two criminals wearing helmets rushes up from behind. One of the criminals jumps off and steals the keys from the first moped and motions for the victim to get off his bike so he can complete the theft. The victim does not get off his bike.

The criminal then jumps back on his own moped as pillion presumably with the intention of returning later to steal the bike (he now has the keys).

The van driver sees what is going on and rams the criminals’ moped before they can drive off. Both fall to the ground, recover themselves and drive off.

Was the van driver committing a crime under UK law? If so is there anything lawful he could have done to interrupt the crime?

If not, at what point does an intervention become unlawful?


  • What is a pillion?
    – ohwilleke
    Nov 13, 2017 at 4:40
  • A second seating position on a motorcycle or horse.
    – 52d6c6af
    Nov 13, 2017 at 9:18

1 Answer 1


Almost certainly not

The Crown Prosecution Service has this guide on self-defense.

A person may use such force as is reasonable in the circumstances for the purposes of:

  • self-defence,

  • defence of another,

  • defence of property,

  • prevention of crime, or

  • lawful arrest.

In assessing the reasonableness of the force used, prosecutors should ask two questions:

  • was the use of force necessary in the circumstances, i.e. Was there a need for any force at all? and
  • was the force used reasonable in the circumstances?

It is arguable that the third-party intervention was for the purpose of defence of property or prevention of crime but this is by no means certain. Notwithstanding, in the circumstances, it is not clear that any force was necessary to achieve these objectives and even if it was, the use of a motor vehicle as a weapon is clearly excessive where there is, as here, no imminent risk of physical harm to anyone.

  • OK. So the van driver here is committing a crime (battery?) in a clear attempt to enact natural justice (bringing criminals to apprehension - I guess this would fall under “lawful arrest” per your link). He moderates the velocity of his vehicle to merely knock them off their bike. Does the law leave room for discretion or must this person be prosecuted for the offense if one of the criminals wants? A criminal is rarely going to simply stop and say “ok you got me!”, so some force will typically be needed in the apprehension. A person is not strong enough to stop a motorcycle, but a van is.
    – 52d6c6af
    Nov 12, 2017 at 22:28
  • 1
    You use the measure of whether force is reasonable as whether there is imminent risk of physical harm, but by your own link, there are other categories of situation where reasonable force is permitted (eg prevention of crime / lawful arrest).
    – 52d6c6af
    Nov 12, 2017 at 22:33
  • If the answer raises additional questions for you, please ask them as questions rather than asking questions that need detailed answers in comments. Please link your new question to this question.
    – Dale M
    Nov 12, 2017 at 22:37

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