While reading the Wikipedia article on Polari, I was struck by the similarities between Polari words and these used by the Droogies in Clockwork Orange. Does anyone know if there are any links between the two?
Burgess would certainly have been aware of Polari, and may even have been inspired by it, but Nadsat is his own invention. It is a language of youth rebellion (nadsat itself is taken from the Russian "-teen" numerical suffix).
When he published A Clockwork Orange in 1962, Russia and the West were in the depths of the Cold War, and it seems likely that the choice of Russian was meant to be especially shocking to his audience. Young people normally acquire their own language stylings to distance their generation from their parents', and elements are often meant to shock and disturb the older folks. There could have been few such attempts more shocking to the elders of that period than Nadsat. Moreover, the made-up language has an ironic aspect as well, since the British political forces in the book are moving toward a totalitarian system such as existed in the Soviet Union.
Burgess was himself a linguist by training and a polyglot (he translated Eliot's The Wasteland into Persian, for example, and other works into Malay). He also created the Stone Age "language" used in the film Quest for Fire, and wrote a critical exegesis of James Joyce's use of language (Re:Joyce). So to say that he "borrowed" from Polari (which your own referenced article reports as comprising Italian, British rhyming slang and thieves' cant — no Russian there) is somewhat misguided, I think, or at least barking up the wrong древо. The resemblance between the two "languages" is only in that they are used for roughly the same purpose — to establish and maintain in-group/out-group identity and status.
From the Wikipedia article for 'A Clockwork Orange':
The book, narrated by Alex, contains many words in a slang argot which Burgess invented for the book, called Nadsat. It is a mix of modified Slavic words, rhyming slang, derived Russian (like baboochka), and words invented by Burgess himself. For instance, these terms have the following meanings in Nadsat: droog = friend; korova = cow; gulliver ('golova') = head; malchick or malchickiwick = boy; soomka = sack or bag; Bog = God; khorosho ('horrorshow') = good; prestoopnick = criminal; rooka ('rooker') = hand; cal = crap; veck ('chelloveck') = man or guy; litso = face; malenky = little; and so on. Compare Polari.