This is a fascinating question to which I'm afraid I can only offer an incredibly unsatisfactory answer: No to all the above. The point of why these items in particular were listed was directly addressed on the 14th November 1988 by the Earl of Dundee, Lord Scrymgeour, I believe in his capacity as a Lord-in-waiting (whip) for the Conservative Party.

He notes that the number of crimes involving these weapons are small, but that that the ban rests 'less on direct evidence of misuse than on the conviction that the items involved are quite beyond the pale'. The Government's position was that these kinds of weapons increased the level of fear in society and contributed to a climate of violence, and since they have no legitimate use except for for violence they should be removed from circulation.

The full list of weapons was drawn up in consultation with Government departments, trade organisations, private companies, sports bodies etc and it seems from the Earl's comments that the aim was simply to describe as many weapons as possible which had no legitimate use apart from violence. I suspect that several of the organisations consulted asked the same question as you, as the Earl mentions that there were doubts expressed as to the legitimacy of these weapons. His full speech can be found here and it's surprisingly interesting - one Lord even expresses concern over whether he'll be able to continue to carry around his own swordstick.

I'm honestly disappointed not to have uncovered a spate of crimes committed by ninjas, but I hope you find the answer useful all the same.

1/2

That’s such a cool question!

u/nmcj1996’s answer explores aspects of legal history that are vitally important. There are aspects of social history that are equally important.

As social context, in 1990 the NES video game Ninja Gaiden was scheduled to be released in the UK but that release was delayed until 1991 and eventually happened under the name Shadow Warriors because the original name was considered inappropriately violent. In 1990 Teenage Mutant Ninja Turtles, which began airing in 1987 in the US, was one of the most popular media properties among school children in Britain (I can remember being 5 and the obsession we had with it on the school playground). 250,000 turtles were imported into the UK to meet the demand for them as pets on the back of the show (1)(2). And the show was released in Britain under the name ‘Teenage Mutant Hero Turtles’ because of the belief that the word ninja was inappropriately violent in media for children. The show was also heavily edited to downplay the use of weapons but specifically, and this is important, the most objectionable weapon in the minds of the censors was not Leonardo’s swords or Raphael’s sais but Michelangelo’s nunchucks/nunchaku. It reached the point where eventually, from the third season onward, he was instead given a grappling hook worldwide and the show placed less emphasis on weapon use. (3)

Compare the opening of the show as it aired in the USA:

https://www.youtube.com/watch?v=AxuvUAjHYWQ

To the one edited/censored for British audiences:

https://www.youtube.com/watch?v=H3x0a8xU1jc

And pay particular attention to the way it is edited to avoid specifically showing Michelangelo’s weapons and their usage and to reduce their depiction in a number of places. It’s interesting that the nunchaku were taken as the most dangerous, or sinister, of the weapons to expose children to and it speaks to an existing discourse that had grown up in the UK around that weapon specifically and 'ninja' and martial arts weaponry as a broader category.

From the examples already shown we can pretty clearly say that if the question is whether there was a contemporary discourse of censorship, and a moral panic, in Britain about ‘ninjas’ at the end of the 80s and the early 90s then the answer is simple: yes.

It was not something that only sprung up around the Ninja Turtles and Ninja Gaiden and was already pre-existing within British media discourse and censorship laws at the time of the 1988 crime bill weapon laws. Exactly why that was the case and the strange specificity of the discourse around certain weapons requires more unpacking, however, and reveals an idiosyncratic and notable episode in the history of censorship in Britain.

Returning to the weapons of choice for Michelangelo, one of the most telling passages in the political debate in the Lords which u/nmcj1996 linked (4) might appear quite unremarkable on the surface but is like the shadow cast by a media/societal discourse in Britain at the time about martial arts, and martial arts weaponry, that highlights it as being far from accidental:

“In considering the range of martial arts weapons, we learnt that the weapon known as a rice flail (or nunchaku) has a legitimate use as a training aid in certain recognised classical martial arts disciplines, and that it is regularly used by thousands of reputable enthusiasts. On balance, we concluded that their supply should not be prohibited.”

On the one hand this is a sober and sensible decision being reached based on evidence of actual usage. On the other hand it is a justification being made because it HAS to be made in the social contexts of British institutional attitudes to ‘martial arts’ weaponry at the time. There was an active moral panic that existed around such weaponry and, specifically, around nunchaku in particular.

I would argue that that moral panic was largely codified around the practices of a specific institution: The British Board of Film Classification, that was, and continues to be, the official body of classification and censorship for film in Britain and in the past that control would also extend to television and even video games.

In simple terms the Criminal Justice Act debate in 1988 on offensive weapons has to include specific mention of consideration of the prohibition of nunchaku, even if that measure is ultimately rejected, because, concurrently, the British Board of Film Classification had a specific ban on the depiction of nunchaku in media altogether. It was a ban that had begun in the late 70s and would be extended all the way until the late 1990s. The BBFC also placed a similar ban on multiple other weapons, for example on the balisong/butterfly knife which is one of the other weapons named in the 1988 law. The BBFC had banned that in 1984 with Streets of Fire being one of the last films allowed to depict one before butterfly knives were added to the list of banned weapons in films (5).

It is also an especially interesting discourse to examine because it revolved so much around the tastes of a single man – the secretary and later director of the British Board of Film Classification from 1975 until 1999, James Ferman.

In Censored: The Story of Film Censorship in Britain Tom Dewe Mathews describes a situation in which the banned weapons list of the BBFC grew longer and longer and less moored in reality, or legality, and rather was concerned with what possible audiences might emulate or find especially glamorous. Bowie knives, such as those used by Rambo, were legal weapons to own but were added to the list of weapons which shouldn’t appear on film. “Presumably due to its lack of military sanction, if not its legality, the Rambo knife then joined what was a growing list of prohibited weapons on the screen. These now comprised Ninja Death Stars, spiked knuckledusters, metal claws, butterfly knives, lighted aerosols, crossbows, and telescopic catapults. But what had begun as a reasonable as well as a politically sensible response to actual incidents in which people were harmed, now entered the realms of the surreal.” (6)

You’ll note the mention of catapults which were again specifically mentioned as being considered in the legal debate surrounding the 1988 law but then were rejected for actually having ‘legitimate’ uses.

In their own telling of their history the BBFC describes a situation whereby there was a “blanket ban of martial arts weaponry” in film by the end of the 80s and early 90s (7). It also suggests what the origin point was: the runaway popularity of Bruce Lee in the 1970s as the inception for a great deal of late twentieth century Asian martial arts culture in the West. An ongoing, although not massively prominent, discourse of moral panic in relation to the martial arts craze throughout the 70s and 80s has been noted by researchers on both sides of the Atlantic including in a book by Chris Goto-Jones which is worth checking out for parallels between video game moral panics in relation to violence and those for film. (8)

The beginning of the formulation of martial arts weaponry as being especially verboten and dangerous in the UK dates back to the reception to Enter the Dragon in 1973. Under the auspices of Stephen Murphy, then BBFC secretary, it was immediately given an X rating in the UK, the highest possible rating, due to its presentation of violence purely as entertainment. It also had a number of mandated edits for violent combat techniques. This meant that it was only intended for adult audiences with anyone under 18 not allowed to view it and under the ‘X’ classification was considered even more extreme than the ‘18’ rating. At the time those edits didn’t include the nunchaku.

The decision to allow the film at all was criticized in the press with focus being placed on fears that it was dangerous and “could encourage people to try kung-fu for criminal purposes” (7). Media coverage concentrated on the young teenagers that got caught up in the craze for martial arts and viewed such films. Public concerns, and media discourse, focused especially on spread of usage of the nunchaku in particular, and other martial arts weaponry, “among London youths”. Fraser Elliott’s PhD thesis on the spread of Chinese Cinemas in the UK noted a number of newspaper stories tying shuriken and nunchaku to football hooliganism and to schoolchildren making makeshift versions of the weapons. Kung fu had “reached well outside of specifically cinematic spaces and had become folded into a narrative of class conflict, truant children and violent football fans” (9) Were these weapons especially more deadly then others that people had access to such as knives? Not really. But the media discourse especially chose them out as a site of moral panic.