Do you think HMRC would interpret asking for further information before continuing such as what bank/account are they referring to?
They would probably come to the conclusion that you want to limit the information that you give them. It's often a game of cat and mouse ... and they may well know more than you realise.
I also have a problem with providing the information as internet accounts don't provide this summary. Although I still think their figure looks wrong.
I thought financial institutions were required to provide annual interest certificates by law. Can't you get the information via on-line statements?
Alternatively I could just list the accounts/details.
It will be easier in the long run, and will influence the level of penalty (if charged).
The reason for the omission is genuine but how should it be "phrased"?
Clearly and simply. And honestly.
I assume it's too late to file an amendment...
You can amend your return, but legislation prevents the amendment being effected until the enquiry is concluded (it can form part of the enquiry conclusions).