Assassination of individuals by the state

I wrote to my MP (via writetothem.com) about the British government assassinating people they suspected of planning terrorist attacks. He replied saying that the government believes the action was legal, proportional and necessary. Part of this justification was based on the fact that circumstances in Syria make it difficult to disrupt attacks in other ways. He stated the people killed were recruiting ISIL members and planning specific attacks in Britain. He also stated that this action was unconnected to general military action against ISIL in Syria.

My reply is below. Feel free to re-use and adapt it if you want to send a similar letter.

Dear Philip Hammond,

Thank you for your reply to my letter about the assassination of Junaid Hussain and Reyaad Khan.

I have 4 questions:

1. When did the British government start assassinating individuals suspected of planning terrorist attacks?

2. What standard of evidence is required to assassinate someone?

3. How imminent must a suspected attack be to warrant assassination?

4. What oversight is there of each decision to perform an assassination?

I continue to believe this practice is in conflict with British values and international law. You mention the UN Charter: I assume you are referring to Article 51 of the UN Charter, which refers to "armed attack" against a country. I do not accept that an individual suspected of planning a terrorist attack falls under the definition of an "armed attack" which was surely a reference to warfare by state-like entities, rather than plans being made by individuals to commit acts well-covered by UK criminal law.

We celebrated the 800th anniversary of Magna Carta in your constituency this year. Our reasons for celebration included the limitation of the state's power over the individual. When the state executes individuals without trial or even publication of evidence, is there any practical limit to its power?

Yours sincerely,

Andy Balaam