This is one of the many complexities to be faced after Brexit and fortunately the ADHB has produced an excellent guide to the subject authored by Sarah Barker and John Knight: Horizon study
After the referendum, I heard that some arable farmers had voted for Brexít because of restrictive pesticide regulations. However, this study concludes: 'The regulatory burden might not be reduced as much as farmers hope and in any event would probably take a number of years to achieve. It is also likely that environmental, consumer and public health lobbies will continue to be influential and to exert pressure for more stringent regulation'.
The report sets out four options. Aligning with the EU would be relatively straightforward, provided it was accepted by the EU. The precautionary principle would continue, but the UK would have no influence over the approval process which might become more restrictive with the remaining EU members.
Aligning with the US has found favour in some quarters because of the use of a risk-based approach there. More actives and products would become available to the UK industry and more biologicals would be available [the US has been particularly innovative in this area]. However, there might be a pressure group reaction to a more permissive regime and climatic differences may mean that US actives are less suitable for use in the UK, particularly for niche crops.
Adopting OECD standards, which use a risk-based approach, might work in the future but there are major challenges in obtaining efficient collaboration between multiple governments.
The UK could have its own policy which would give it full control of the approvals process. It could adopt a low-risk approach and it might be possible to speed up the approval of biopesticides. However, the registration and use of pesticides would have to be acceptable to trading partners. The UK may be seen as too small a market for companies to go to the expense of registering products for approval, leading to fewer actives being available.
In other words, there is no ideal solution, although a UK policy might be seen as politically compatible with hard Brexit.