Pick something that you do not like in people and chances are that Mr. Lockton is also that way. Is he a liar? Yep, he has got that one covered in spades. He lies to just about everyone, and they are not little lies either. He is a loyalist through and through, but he acts like a Patriot when it benefits him.
Maybe that is not mean enough for you though. Try this one on for size. He is verbally and physically abusive to his wife. In chapter 13 Mr. and Mrs. Lockton get into a huge argument. Mr. Lockton, wanting to get his way, starts throwing various household objects at his wife. I also believe that Mr. Lockton does and says things to Mrs. Lockton just to make her mad. For example, Mr. Lockton sends Isabel to Lady Seymour's house to help her out. Mr. Lockton does this for some selfish reasons, but he also does it knowing full well that Mrs. Lockton is going to be livid about it.