I can give some guidance on what is required by the EBS ID Panel with regard to Essex "Notes" (and also "Description") species:
Notes = Required for species that are scarce, but annual in Essex and relatively easy to identify given sufficiently good views and experience of the species. A brief description on how the species was identified, including comment on awareness of and exclusion of possible confusion species.
Description = Species less than annual in Essex, including almost all former BBRC species. The description should be more detailed than for a "Notes" species, e.g. full details of plumage, calls and behaviour, consideration of similar species and how they were eliminated at the time of the sighting and all relevant background details to demonstrate that the identification is sound.
In both cases, it is extremely helpful to the ID Panel and really aids the assessment process if observers complete a "Rarity Report Form". I have attached a template (in word format). This might seem like overkill for a "Notes" species, but if all the sections are completed it gives the ID Panel almost all of the information they are likely to need in one document. One of the main reasons why records of Essex rarities are found "Not Proven" by the ID Panel is simply lack of information and detail.
Sketches, photos, video and sound recordings are also invaluable to the ID Panel in the assessment process and should be included in the record submission where possible.
As Stewart indicated, the latest EBR gives guidance on what species are "Notes" and "Description" respectively. Descriptions should be sent to the Essex County Recorder, Les Steward, who then sends them to the ID Panel for assessment.
An article on the EBS ID Panel explaining what it is, what is does, etc and giving actual examples of accepted "Notes" and "Description" records was published in Issue 116 of Essex Birding (Summer/Autumn 2010).
I hope that helps.
Cheers
Paul