What went wrong with National Crime Agency warrants?
The National Crime Agency (NCA) has launched an internal inquiry into the way warrants are applied for following the collapse of major court trials.
The NCA said it was prompted by issues found with warrants in two cases that went before the courts, Operations Heterodon and Enderby.
The issues came to light following an investigation by the news site Buzzfeed.
Buzzfeed investigations reporter Tom Warren explains the story.