Familyskeletons, "Mine" was actually William Whiteley ISHERWOOD", not Sherton - but that was an aside from your main point about middle names.
A young friend of mine recently got married, and after the event, decided to "keep" her maiden surname, as an additional middle name to be followed by her married surname. Apparently she had to do it by deed poll, - I'd thought she could just say she wanted to be known as......".......". But she actually did that, I know because she asked me to sign it. I was most surprised.