Broadly, the pan-European targeting of complex cross-border criminal activity is founded upon inter-governmental cooperation as much as it is upon specific EU law frameworks. Where this legal foundation remains unchanged, most importantly the European Court of Human Rights and the Council of Europe, cooperation and participation in these cross-border endeavours will continue.
EU crime agencies
There are two EU agencies that explicitly require membership of the EU for participation: Europol, the EU police intelligence agency, and Eurojust, the coordinating network of EU prosecution agencies. A negotiation will be required to establish a new legal foundation for the UK’s membership of, or cooperation with, these bodies. Issues of data protection in the sharing of intelligence information will also require resolution, as the UK will be outside the EU regime following Brexit. But it is unlikely that either the UK or the EU will want to see any reduction in cooperation in investigating criminal activity and it can be expected that a relatively early resolution of these issues will be found. Other non-EU states, such as the USA, Canada, Australia and Norway, have developed relationships with Europol and, with its geographical proximity, it seems very likely that the UK will too.
Mutual legal assistance
The UK can offer judicial assistance to any country or territory in the world, regardless of the existence of an agreement providing a framework for such assistance. The only stipulation is that if there is such an agreement, any request be made within the framework provided.
The European Union based its framework of cooperation on a protocol negotiated by the Council of Europe. Consequently, the UK will be able to rely upon this pre-existing agreement, as the UK’s membership of the Council of Europe remains unchanged. However, this protocol does not provide the specific mechanisms or detail that was created under the European Union framework. For example, the European Investigation Order (EIO), seeks to allow the transfer of evidence through a single instrument prescribing detailed methods for gathering evidence. The Regulations introduced by the UK in 2017 to implement the EIO (Criminal Justice (European Investigation Order) Regulations 2017) will be revoked on the UK’s withdrawal from the EU, albeit that orders issued prior to the withdrawal will remain to be complied with.
Whilst some detail for the process of mutual assistance is provided under the 1978 protocol, the impact of Brexit will be for subsequent requests from, and of, EU members to become ad hoc and the outcomes less predictable. This may lead to delays and potentially inconsistent treatment of requests for mutual legal assistance. The ultimate solution is likely to be a bi-lateral treaty between the UK and the EU, as the UK has had with China since the beginning of 2016.
See here for detail on how data protection will be affected by Brexit.