Major Boyd was a British officer stationed in the British zone of West Berlin during the time of Biggles Follows On. Although his appointment is never given in the text, it can be surmised that he is an intelligence officer of some kind. He is described as "an elderly man in civilian clothes", yet works in a British military building with an Army sergeant in attendance.
When Biggles calls on Major Boyd shortly after arriving in West Berlin, Boyd was already expecting him, having received a signal from London. Biggles asked Boyd to lend him a guide to get him through to the Hotel Prinz Karl in the Zindenplatzer without having to go through any checkpoints.
Boyd's conversation with Biggles reveals a lot about his character. Typical of a professional intelligence man, he doesn't get excited or inquisitive about Biggles' request. He had probably seen many of such requests before. He understood the principle of "need to know", and did not pry into the details of his colleague's case. He supplied the guide as requested, limiting his questions merely to operational issues like how long the guide should wait for Biggles and when Biggles wanted to set off. Nor does he comment or otherwise give unsolicited advice beyond telling Biggles that it shouldn't be too difficult to get to his destination and asking if Biggles would need any help if he should get into trouble--an offer which Biggles declined.