What AI got wrong, and what AI caught.

Asked how to split £25,000 across a cash ISA and a stocks and shares ISA (the real 2026/27 allowance is £20,000, frozen since 2017), ChatGPT never flagged the false figure. It used £25,000 throughout, splitting it into example allocations like '£7,500 Cash ISA + £17,500 Stocks and Shares ISA'. No web search fired. The same account's ChatGPT caught a different false premise (a stated £2,000 Personal Savings Allowance, versus the real £1,000) moments later where a search did fire, citing gov.uk. Claude, Gemini, Perplexity and Grok all caught the £25,000 error under identical default conditions.

Asked for the maximum UK handheld-phone driving fine with a source, Gemini (Pro) attributed the £2,500 lorry and bus figure to Police.uk, the find-your-force and crime-data portal, which has no remit for legislative fine schedules. The number was right, the source had nothing to do with it, and there was no hedge.

Asked how many free childcare hours a working parent of a 9-month-old in England gets right now, Perplexity said 15 hours and described the 30-hour rollout as still to come, ten months after it completed. It cited a real Feb-2025 gov.uk page, and another of its own cited gov.uk sources states the opposite. On a same-day re-run it self-corrected to the right 30 hours, so the failure is intermittent, not fixed.

Asked flatly who would win, Claude was the only one of the five to stop and reframe the question before answering, flagging that with the tournament at the quarter-final stage this was now 'a live read rather than a preseason guess' rather than the open-ended punt the question sounds like, then gave its pick on current form.

On the stamp-duty question, ChatGPT opened with 'Assuming you mean England or Northern Ireland' and noted that Scotland and Wales use different property taxes, without being asked, and cited only the correct gov.uk page. Six questions, six clean citations.

Grok cited the single correct gov.uk page on all six questions with no commercial or secondary sources mixed in, and flagged the Scotland and Wales tax divergence unprompted. It was the cleanest sourcing of any assistant tested.