The most reported AI mistake in legal work is the fabricated authority. A general model, asked for support, will often produce a citation that looks right in every respect except that the case does not exist, and it will reach your advice unless a check catches it. The wording is plausible, the court and the year are convincing, and the whole thing is invented.
Why it happens
A large language model generates text by predicting what tends to follow what. It holds no index of real cases and no sense of truth. Having seen many citations, it can produce something shaped exactly like one with no guarantee that the case behind it is real. Confidence in the output is no signal of accuracy.
What it has already cost
In England the High Court has addressed this directly. In R (Ayinde) v London Borough of Haringey, decided in 2025, a Divisional Court led by the President of the King's Bench Division dealt with submissions that cited authorities which did not exist. The court referred the lawyers responsible to their regulators, the Bar Standards Board and the Solicitors Regulation Authority. The court was plain that putting a fabricated case before it, whether through dishonesty or a failure to check, can be a serious breach of duty with real consequences. A widely reported United States case in 2023 had already sanctioned lawyers for the same failing. The duty to verify what you put before a court has not changed, and not understanding how the tool works is no defence.
The checks that hold
Treat every citation, quotation and figure from a general model as unverified until a person confirms it against a real source. Where research matters, prefer tools built on a known legal database that link to the underlying authority, so the source can be opened and read. Record that the check was done. A fabricated case that reaches a letter is an embarrassment. One that reaches a filing is a regulatory problem.
Used with a human reading every source, these tools speed up the search. They do not replace the judgement that decides what is real.
The judiciary’s AI guidance shows how seriously the courts take what reaches them.
If nothing currently stands between a fabricated authority and your advice, we build the checking habit with your team in an afternoon: get in touch.