Dick Turpin, Two of a kind, you scratch my back, I'll scratch yours

Dick Turpin, Series 02, Episode 03. The Blood Money

Dick Turpin: Look at them. Two of a kind.
Swiftnick: What do you mean?
Dick Turpin: Well, you scratch my back, Colonel de Coursey and I'll scratch yours.

(Two/three, etc of a kind = two/three, etc people or things that are very similar)
(You scratch my back, I'll scratch yours = used to say that you'll help someone if they agree to help you)

Dick Turpin, How sharper than a serpent's tooth it is to have a thankless child!

Dick Turpin, Series 1, Episode 12. The Hostages

Sir John:  How sharper than a serpent's tooth it is to have a thankless child! William Shakespeare, Hamlet, you know.

Jem: King Lear!

Sir John: If I say it's Hamlet, then it's Hamlet! You presumptuous young puppy!

(serpent = a snake, especially a large one - literary)
(hostage = someone who is kept as a prisoner by the enemy so that the other side will do what the enemy demands)

You can learn more about this saying here The Phrase Finder
And of course it's King Lear, Sir John! 

Dick Turpin, The wish is father to the thought

Dick Turpin, Season 1, Episode 8. The Upright Man

Dick Turpin: To the upright man!

Tyson Sarney: Dick! By Heaven! Oh, thank God you're back! We thought you'd    been captured.

Dick Turpin: And the wish is often father to the thought.

(which means that the thought is born from the wish, because the "upright" man has betrayed Turpin and he's astonished to see him back) 

(upright: always behaving in an honest way)

To learn more about this saying do visit the english club related page.