E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
has its name from a gate set up there about 400 years ago, to receive tolls for the bishop of London, when the old miry road from Grays Inn Lane to Barnet was turned through the bishops park. The village being in a high or elevated situation explains the first part of the name.
Sworn at Highgate. A custom anciently prevailed at the public-houses in Highgate to administer a ludicrous oath to all travellers who stopped there. The party was sworn on a pair of horns fastened to a stick
(1) Never to kiss the maid when he can kiss the mistress.
(2) Never to eat brown bread when he can get white.
(3) Never to drink small beer when he can get strongunless he prefers it.