Its much touted now as a cure all and evidence of some sort of professionalism, but insurance doesn't guarantee anything except the fact he has insurance.
In fact, unless you are intending to sue him for professional negligence, you won't need to know about his insurance.
Personally I'd prefer a competent architect with no insurance than a fool insured out to the gills.
And teh best way to assess competence is see his work and seek referecnes from clients.
I'm not sure its mandatory to be insured now and certainly years ago it wasn't - it was subject insurance being available at competitive rates,
The amount usually related to the value fo the work insured, whether you were in partnership and whehter some or all of it was abroad.
That having been said we seem to be suffering frmo over qualification in all fields so I've no doubt insurance is a must.
I think most competent firms can get cover up to 1.3 Million quite affordably.
Ask him to confirm it it writing and copy you his certificate of insurance.
I've never done this personally, but then I've never been asked.
ONQ.
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All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.