It could be an offence under section 5 Public Order Act 1986:
(1) A person is guilty of an offence if he—
- (a) uses [...] disorderly behaviour ...
within the hearing or sight of a person1 likely to be caused harassment, alarm or distress thereby.
Causation to consider, which is:
whether the defendant's conduct (or omission) caused ... harm or damage.
And also recklessness, which can be described as:
In R v G  1 A.C. 1034 two boys set a fire which caused significant damage. They were charged, and convicted, for reckless arson contrary to section 1 of the Criminal Damage Act 1971:
(1) A person who without lawful excuse destroys or damages any property belonging to another intending to destroy or damage any such property or being reckless as to whether any such property would be destroyed or damaged shall be guilty of an offence.
(3) An offence committed under this section by destroying or damaging property by fire shall be charged as arson.
This conviction was quashed by the House of Lords who determined that test of recklessness for criminal damage is subjective and should take account of, for example the defendant's age (in R v G they were 11 and 12). The court determination was:
A person acts recklessly within the meaning of section 1 of the Criminal Damage Act 1971 with respect to -
(i) a circumstance when he is aware of a risk that it exists or will exist;
(ii) a result when he is aware of a risk that it will occur;
and it is, in the circumstances known to him, unreasonable to take the risk.
But compare this with DPP v Newbury and Jones  AC 500 if someone were to die as a result of being hit by a brick:
The defendants, both teenage boys, had thrown a piece of paving stone from a railway bridge onto a train which had been passing beneath them. The object struck and killed the guard who had been sitting in the driver’s compartment.
The defendants were convicted of manslaughter, and unsuccessfully appealed, on the ground that they had not foreseen that their actions might cause harm to any other person. Lord Salmon explained that a defendant was guilty of manslaughter if it was proved that he intentionally did an act which was unlawful and dangerous and that act caused death, and that it was unnecessary that the defendant had known that the act in question was unlawful or dangerous.
1Note that there has to be such a person, not a hypothetical one, to be guilty of this offence.