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I don't think there's a law that names anti lag as such, but I think it's fair to say every anti lag system I've come across would certainly fall under the remit of Section 59, "vehicles used in manner causing alarm, distress or annoyance"
The wifes daily driver has ALS and with the stock cat on doesn't alarm or distress anyone but is still quite effective.
I have tuned cars equipped with ALS where it absolutely could cause offence, but it doesn't have to.