The Plant Health (EU Exit) Regulations 2019

7.  The boundary of the buffer zone must be at least five km beyond the boundary of the infected zone, but may be reduced to one km beyond the boundary of the infected zone where the appropriate UK plant health authority concludes with a high degree of confidence that the initial presence of the plant pest has not resulted in any spread of the plant pest and the following conditions have been met—

(a) all host plants within a radius of 100 m of the infected plant have been promptly removed;

(b) no other plants have been found infected by the plant pest in the infected zone following official tests which have been carried out at least once during the course of the year and which targeted symptomatic plants, as well as asymptomatic plants in the proximity of the symptomatic ones;

(c) a delimiting survey has been carried out in the zone surrounding the infected zone that extended at least 2.5 km beyond the boundary of the infected zone, which included visual inspections of susceptible plants and the sampling and testing of symptomatic plants, as well as asymptomatic plants in the proximity of the symptomatic plants; and

(d) the possibility of natural spread of the plant pest has been excluded as a result of tests which have been carried out twice during the flight season of the relevant vector and in accordance with international guidelines in which no vectors carrying the plant pest have been detected in the infected zone.