Appears all over British government documents. This explains what it means, in a 2000 Commons committee debate on the Regulation of Investigatory Powers Bill:
“There is the provision for action—the tasking of our intelligence agencies—in the interests of the economic well-being of the United Kingdom. Those who have followed these matters know that that is a well-worn provision. It is in existing legislation, and is provided for in the European Convention on Human Rights. It sometimes causes puzzlement as to what it can mean.
“Examples of where it might be useful are where there is instability in a part of the world where substantial British economic interests were at stake, or where there was a crisis or a huge difficulty about the continued supply of a commodity on which our economy depended.
“The House will notice that the Bill restricts the activities of the SIS and GCHQ for safeguarding the economic well-being of the country to the acts or intentions of persons outside the United Kingdom. […]
“The examples that Douglas Hurd gave are clear. One is coded speak for oil—
“the continued supply of a commodity on which our economy depended.“