I asked my accountant about this last year. He suggested trying it. He said to fill in a self assessment form saying I was in business as a helicopter pilot, and put that I was still training, but in the bit for info ON THE SECOND PAGE. According to him, that way they might not query it, as they rarely look beyond the first page. They only have 18 months to query it, he said, after that they have to accept it. And he assured me the worst that could happen would be that they told me I couldn't do it. So far I've heard nothing, and am about to claim more expenses for this year. In a year or two I might have your answer. But it seemed worth a try.
Maybe both of us will get a beter answer here.