PinkDalek wrote:This 2015 article from The Telegraph suggests Whether you report it or not, HRMC says it will spot the mistake and make contact with you. Throughout the year Isa providers report how much each of their customers has invested so HMRC has this information. … A spokesman for HMRC said those who break the Isa limit should “sit tight and expect contact”.
That's interesting because usually HMRC would suggest that it is better to own up to mistakes, because then at least it looks like an honest mistake rather than you were trying to get away with it.
Sounds like HMRC are just assuming that it's always an honest mistake, no big deal, and some kind of adjustment will be made without prejudice. And they are usually not that charitable.
It also sounds like they are highly confident that they will always pick up on this. I can only assume they can run automated checks by NI number, since you now need a NIN to open an ISA (you did not need one back in the day).
I only have one ISA provider so it would be impossible for me to make such a mistake, but I am surprised that HRMC appear so sanguine about it. Then again, there are not large tax savings for most ISA investors anyway.