Yes

If someone perpetrated an attack take them out. If not then you cannot murder someone on the assumption they will do something regardless of intel.

The political and social reaction to foreign assassinations could lead to war, public outrage and a collapse of British values that would destabilise internal public opinion and politics. Assassinations also lead to justified retaliation.

We must assume that any action taken by an individual country will be replicated by other countries, and it can only ever result in escalation

By eliminating people like Al-Baghdadi, Solemani etc.
We have shown that we (NATO and the west) are not to be messed with, and injustice will be met with violent retalliation.

Out County has no right to assassinate foreign diplomats or citerzens unless they have committed a hanosue crime against the people of out nation.