[holding answer 3 July 2009]: The main focus of expertise in DEFRA for the fields listed is at the Food and Environment Research Agency (Fera).
Fera employs the following numbers of specialists in the fields covered by the question:
Specialism Fera employees Lepidoptery 3 Botany 3 Lichenology 0 Bryology 0 Mycology 6
Fera has high levels of staff retention in the three specialisms in which staff are employed and, as a consequence, has no plans to recruit to these areas in the foreseeable future.