Lowest tracker margin known?

[Brendan Burgess]

The customer had an ECB + 0.45% rate.

So the customer had a normal tracker mortgage but the bank input the margin incorrectly.

I presume that they corrected it when they noticed it and then charged the customer 0.45%.

So it does not change the answer to this question "What was the lowest margin?"

 

[ClubMan]

But the Mortgage system had a manual input area where a positive or negative margin could be applied.
It was a functionality that was not used business wide but was accidentally used on a handful of mortgages due to incorrect use.
When ECB went to zero it was noticed that some interest postings to some mortgages were negative and therefore crediting payments to the mortgage due to the margin putting the active rate into a minus.

I'm very skeptical about this. Surely it would've been mentioned somewhere before now? Extraordinary claims require extraordinary proof to be believed.