Hi Mike
I'm clueless on culling rats in such a situation, but if you are going to follow the advice to protect the hives with wire netting, remember the risk of Weil's disease entering through cuts to the skin. Rats spread this potentially fatal bacterium in their urine, and the disease is certainly in the UK.
http://www.leptospirosis.org/http://www.hse.gov.uk/pubns/indg84.pdf
best wishes
Gavin
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