Lol no that would be reasonable and that doesn't exist anymore in this timeline.

Likely if he had done it to people he knew, and by extension that this particular prank wouldn't excessively affect them negatively.

Pranking your friends in public, poor taste, but possibly acceptable. Pranking random members of the public, at what could be the worst time of their life...

Mate, he didn't have his nuisance license. As punishment he will now be forced to observe the 3pm tea alarm with a glass of luke warm water.

I expect it would be for things like mental health, cultural / religious, or practical reasons i.e. shouting really loud can land you an ASBO if you do it for no reason, but not if it's part of psychotic episode, call to prayer, or an attempt to alert people to danger.

How is "because it was funny" not a reasonable excuse in this one instance?

"...pleaded guilty to causing a nuisance without reasonable excuse"

thats a crime?

https://en.wikipedia.org/wiki/Public_nuisance

The nuisance action began in twelfth century England as a criminal writ, belonging only to the Crown. It was used in cases that involved encroachments upon the King's land or the blocking of public roads or waterways. The King sought to punish these criminal infringements, commonly known as "purprestures", through criminal proceedings. Over time, activities prosecuted as public nuisances included everything from embezzling public funds to having a tiger pen next to a highway, from assisting a homicidal maniac to escape to placing a mutilated corpse on a doorstep, and from selling rotten meat to "subdividing houses to the point where they become 'overpestered' with the poor". As these examples demonstrate, early authority to commence public nuisance actions was derived from the sovereign's "police power".[10]

Spencer (1989 at 59) describes the offence as "a rag-bag of odds and ends which we should nowadays call 'public welfare offences'".[11] But the common feature of the crime is that members of the public suffer a common injury through interference with rights which they enjoy as citizens. The modern definition is found in paras 31–40 Archbold (2005):

A person is guilty of a public nuisance (also known as common nuisance), who (a) does an act not warranted by law, or (b) omits to discharge a legal duty, if the effect of the act or omission is to endanger the life, health, property, morals, or comfort of the public, or to obstruct the public in the exercise or enjoyment of rights common to all Her Majesty's subjects.[12]

can we arrest trump for that if he comes back to the uk?

I'm pretty sure that national leaders don't normally visit countries unless they are extended diplomatic immunity, so probably not.

EDIT: Hmm. Though...this says that it was abolished as a crime in England and Wales four years ago. There's still the tort, but the way The Mirror described it, he was "fined", and I think that you only get fined in criminal law, not civil law (in civil law, the analog would be called paying punitive damages, at least here in the US).

A SUCCULENT GRIM REAPER COSTUME?!!

We also have the very catch all of "disturbing the peace". Some friends of mine got done with that because the police had been called despite no actual crime being committed. They were eventually "bound over" for a year which is basically a deferred fine to encourage you not to do anything that attracts the police's attention.