In the short story "The Adventure of the Mazarin Stone" by Arthur Conan Doyle,in a dialogue between Billy, Sherlock Holmes' page, and Dr. Watson:

'I don't mind telling you, sir, but it should go no farther. It's this case of the Crown diamond.'

'What - the hundred-thousand-pound burglary?'

'Yes, sir. They must get it back, sir. Why, we had the Prime Minister and the Home Secretary both sitting on that very sofa. Mr Holmes was very nice to them. He soon put them at their ease and promised he would do all he could. Then there is Lord Cantlemere-'

'Ah!'

'Yes, sir, you know what that means. He's a stiff 'un, sir, if I may say so. I can get along with the Prime Minister, and I've nothing against the Home Secretary, who seemed a civil, obliging sort of man, but I can't stand his lordship. Neither can Mr Holmes, sir. You see, he don't believe in Mr Holmes and he was against employing him. He'd rather he failed.'
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What does Billy mean by saying "Then there is Lord Cantlemere-"? And what does he mean by describing Lord Cantlemere with "stiff 'un"?

Lord Cantlemere is of such people who never trust on anybody. They follow you to the end of the world just to see if you make a mistake, and then comb your hair with a rasp.
These people are a double harm when they end up in being a teacher or military instructor.