You would select this option if you worked for a single limited company / organisation and only submit a SINGLE VAT RETURN.
NOTE:
The one exception to this rule, if you are employed as the accountant for multiple limited companies within the same group, so you are not actually an AGENT you just have authority from each of the companies to act and submit on their behalf, then you would select this option !
Again, if you are unsure please ring support on 0161 660 1366 or 0151 909 5695