What is the problem?
MLA enables countries to use their law enforcement powers across international borders.
Depending on who is doing the investigating, those powers can be coercive, invasive, highly damaging and open to abuse.
Even requests for covert surveillance or a search warrant aren’t subject to independent verification of the facts in the receiving country. Unlike an extradition request, which can only be executed following full judicial consideration in adversarial proceedings, most MLA requests are accepted at face value and executed, without notice to the target, with few procedural safeguards.
Therefore, MLA depends on mutual standards, trust and assumptions of good faith which may not be justified simply because both countries are signatories to a treaty.
In reality, the UK receives hundreds of MLA requests annually from countries where the rule of law is weak and criminal justice is used for improper purposes. Some of these countries may actively be trying to harm UK interests. Nevertheless, the UK has a legal duty to execute the request and limited discretion to refuse.
Obviously, MLA works both ways, so it is in the UK’s interests to assist other countries to ensure reciprocity. That, however, is no comfort to the target of a politically or improperly motivated investigation expecting the UK legal system to protect them from injustice and abuse.
For anyone under foreign investigation, pre-empting, resisting and mitigating the effects of abusive MLA requests are important parts of any legal strategy.