I disagree, I think having a judge have to OK every military operation would be a very good way to completely hamstring our military. The people in question were working for a military force that we are currently at war with. That makes them legitimate targets as far as the military are concerned.
This operation was agreed months ago by the National Security Council. They used military assets but it wasn't a military operation in the traditional sense.
https://www.gov.uk/government/organisations/national-security/groups/national-security-council
https://en.wikipedia.org/wiki/National_Security_Council_(United_Kingdom)
Note the council members, none of which are military, although military members can be part of meetings.
True, a General having to go through a judge before launching a military operation would cause some issues. That however is just irrelevant in this case.