After several YEARS of trying (and no doubt boring you all to death with the saga), I'm overjoyed to be able to tell anybody who's interested that I have finally succeeded in getting my Vietnamese BF a UK Visa.
He has today been issued with a (wait for it....SIX MONTHS) multiple entry Visitors Visa, valid from late December.
My new book "How I Did It" will be published in January 2018 and will feature full illustrated details - meanwhile helpful advice for anybody in the same position can he had free of charge by PM.
Thanks to those SGT members who supported/helped along the way.