Lowest tracker margin known?

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