The Home Office, asserts a paper that I am reading. That cannot possibly be true, was my first thought. But which one it is, then? Department for Environment, Food & Rural Affairs, maybe? Because DEFRA is part of it and often holds public consultations on the use of almost anything to do with genes in plants and non-human animals.

No.

The Animals in Science Regulation Unit (ASRU) is indeed part of the Home Office. Source: https://www.gov.uk/government/collections/animals-in-science-regulation-unit