Bilateral trade deals are negotiated between two countries. Both sides set out what they hope to achieve through the deal and negotiate with each other accordingly until an agreement is reached. In contrast, multilateral trade deals have three or more member countries and the core agreement is negotiated between the original signatories. Countries which join multilateral trade deals later, once the deal is already in existence, are expected to comply with the core agreement.
While the UK can therefore make demands to protect domestic pesticide standards in bilateral trade negotiations with individual countries, it is unlikely to be able to do so when joining a multilateral deal like the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP). In this case (and when joining other multilateral deals) the UK would be acceding to the deal, not negotiating.
Some multilateral deals do have ways for countries to opt out of specific rules included in their core agreement. However, exemptions usually have to be negotiated with all other members and it would be unlikely for the UK to secure unanimous agreement for a broad exemption from all requirements related to pesticides, particularly if a trade deal’s member countries include large agricultural producers.
The UK Government exited the EU arguing that it no longer wanted to be a ‘rule-taker’, and continues to present trade sovereignty as one of the key benefits of Brexit. However, joining multilateral deals like CPTPP with almost no opportunity to change the text of the core agreement would undeniably reduce the level of control that the UK has over its trade policy.