"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 agencies may not and do not get involved in domestic economic, commercial or financial affairs."
So it's not quite as broad reaching as it reads on first glance. It is generally a problem though that laws need to be written so they're broad enough to cover circumstances which might not have been considered at the time of the laws' writing so that new laws don't need to be written all the time yet they can't be so overly broad as to be unworkable - which is why the judiciary has it's role in deciding how to interpret the laws and decide whether or not they ought to apply in a given circumstance.