Is assassination by the UK Government legal?

The Ministry of Defence has sought out and killed some (erstwhile) UK citizens in the Middle East, based on intelligence that, from there, they were actively planning terrorist outrages in the UK. But is that legal and desirable?

Targetted killing may perhaps be justified in times of war, especially when the evidence is compelling. Are we at war?

But is it worrying that the MoD may have taken steps which breach, or at least weaken, UK legal rights for everyone?

The UK did not, for instance, assassinate Saddam Hussein, even though we were at war with Iraq. We support fair trials, eg at the Hague, rather than arbitrary execution, of people who appear to give every evidence of wrong-doing .. but is it conceivable that some apparent traitors in ISIS have been acting under duress?

The death penalty has been withdrawn, even for traitors, in the UK.

So we would like Mr Gove to clarify
a) whether the death penalty has been brought back for treason,
b) whether treason can be proven without a trial (even in absentia),
c) whether the prevention of harm makes targetted assassination legal (overseas or at home),
d) whether assassination of an erstwhile or current UK citizen is legal in any circumstances, and
e) whether the MoD has broken any British or other laws in seeking out and killing particular people (including current, or erstwhile, UK citizens) in Syria and the Middle East , without any form of trial,?