A supplier has invoiced me incorrectly by omitting to charge duty and charging an incorrect (lower) rate of VAT on the supply. What has happened is that the end use of the supply has been wrongly entered on their system, despite me telling them what the end use is, and the end use makes a big difference to the duty & VAT position. If I was registered for VAT I would write to the supplier to point out the mistake and request a corrected invoice. But on this occasion I am merely a consumer. I think many consumers would look at the total on the invoice and if it was what they were expecting (or lower!) they would do nothing. Does the fact that I know the supplier has made a mistake put me in a position where I have a legal obligation to do something about this? Searches reveal lots of references to incorrect VAT in the context of business-to-business supplies but I haven't found a reliable source which deals with business-to-consumer transactions from the consumer's point of view.
By the way, this particular supplier has an incompetent back-office team (nice people, but incompetent) and I think that trying to get them to correct the invoice will be just as difficult as trying to find someone at HMRC who could understand what I am talking about and advise me.