Mike Harding is an agent with MI13.
That is defined for us as "a discrete department within the hidden depths of the Ministry of Defence". Run by Major Challenor, it is elsewhere called "a clandestine special operations unit known only as 'Thirteen' to the few souls who worked within it. The unit comprised a select group of ex-special forces freelance operatives who could be called upon whenever an asset with specific skillset was required. Members of the unit were highly trained, deniable, expendable but not easily replaced, at least not quickly. MI13 operatives were never deployed within the UK, only abroad, well out of sight of Westminster, the MoD, Special Branch, local police and anyone else who might become interested and start asking questions. The department handled the covert, clandestine but entirely necessary operations that none of the other security agencies would touch with a bargepole because what was required was either far too politically sensitive or a risk assessment had determined the operation to be not only exceptionally high risk but with a high probability of failure.
We are given an excellent short bio of Harding in one of his adventures: "At a shade under six feet tall, broad shouldered with the physique of an athlete rather than a body builder, Harding was exceptionally fit for someone in his late forties. His well cut greying hair highlighted the piercing blue eyes set in the unsmiling face of a man who had seen CQB or Close Quarter Battle, at first hand. Since leaving the Army several years ago Harding had lived in a two bed cottage in Woodbridge, a small Suffolk town close to the east coast. The location suited him. It was fairly anonymous, the cottage was easy to maintain and he had few neighbors. All his neighbors needed to know about Harding was he had served twenty two years in the British Army and had been a sergeant in the Royal Engineers. What they did not know, nor did Harding have any intention of telling them, was during that time he had spent several years with the Special Air Service."
While part of the Regiment, as the SAS was called by its members, Harding had seen plenty of action in Northern Ireland and Iraq, and more enough in Afghanistan going up against the Taliban. "It was because of his skills and ability that [MI13] were keen to retain him on a freelance basis after his discharge from the Army".
The first adventure we follow Harding on has nothing to do with his work with MI13 but since he is freelance and only called on when needed, his participation in that activity will not interfere with his government work. The second adventure, after detailing an assignment Harding does for MI13 in Turkey, deals with his discovery of something the US government really did not want seen and the efforts of several of its OSI operatives to keep thing quiet - permanently. The last two adventures (as of now) are definitely MI13-related missions.