Green’s Dictionary of Slang

(UK Und.) highway robbery.

1552		G. Walker Detection of Vyle and Detestable Use of Dice Play 18: Thus they give their own conveyance the name of cheating law; so do they other terms, as sacking law, high law, figging law, and such like.
1608		Dekker Belman of London n.p.: Now must you cast up your eyes and looke aloft, if you have a desire to behold the picture of The High Lawe: which taketh that name from the high exploits that are acted by it: the Schollers that learne it are called High Lawyers; yet they never walke to Westminster to pleade, though oftentimes they are called to the Barre, but then it is to haue them Hold vp their hands, that the Hangman may tell them their fortune. All the former Lawes are attained by wit, but the High Law stands both upon Wit and Manhood. For the High Law is nothing elfe but taking a purse by the High-way side.
1620		‘Song of the Beggar’ in Farmer Musa Pedestris (1896) 14: If a Bung be got by the hie Law, / Then straight I doe attend them.