Ongoing research around the RBCT culling sites also shows that while the benefits of culling within the trial zone persist for some time, the spike in infections around the edges - the perturbation effect - tends to dissipate over time.

BBC: Badgers back in the firing line

The Oxford team reasoned that if this perturbation was so great, it ought to be evident in the sediments of Lake Malawi.

BBC: Toba super-volcano catastrophe idea 'dismissed'

To deal with the potential problem that some farmers might get disillusioned and withdraw early - creating perturbation - each group will have to deposit enough money into a bank account in advance to cover the entire cost of a four-year operation.

BBC: Badger cull heads for further consultation

It is well known that partial culling creates an upsurge of disease due to perturbation of infected badgers, in other words increasing the movements of infection among the population by the badgers scarpering to neighbouring sets, potentially setting up a new geographically infected area.

BBC: Viewpoints: The badger cull