‘Disclosure’ means a disclosure of irregularities. In other words - an admission that an account is wrong. It does not matter whether or not the taxpayer is able to quantify the irregularities at the time the disclosure is made. A complete disclosure will in some cases need to include a description of how the irregularity came about.
Disclosure implies a positive, voluntary and useful contribution to your knowledge of the irregularities. You may, for example, find that a statement made at an early stage of you investigation constitutes disclosure but the same statement, if made at a late stage in your investigation, is little more than a worthless confirmation of what you have already established.
Disclosure does not, in this context, include the production of information and documents in response to your enquiries. These should instead be regarded as elements in arriving at the abatement for co-operation ( IHTM36191).
Examples of the specific things you need to look for when considering disclosure can be found at IHTM36182.