Paragraph 23
The appropriate UK plant health authority need not demarcate an area in relation to a finding of the plant pest in a relevant UK territory where—
there is evidence—
that the infection has been caused by the recent movement of susceptible plants to the area in which the plant pest was found; or
that the plant pest has been found in a site with physical protection from the vectors of the plant pest;
there is evidence that the susceptible plants were infected with the plant pest before they were introduced into that area; and
no vectors carrying the plant pest have been detected in tests carried out in accordance with internationally validated testing methods in the vicinity of those plants.
24. Where the appropriate UK plant health authority does not demarcate an area for the reasons specified in paragraph 23(a) to (c), the appropriate UK plant health authority must ensure that annual surveys are carried out for a period of at least two years beginning on the date of its decision not to demarcate the area, in order to determine whether any other plants are or have been infected with the plant pest.