"Pukka" was adopted as British youth slang a couple of decades ago. It
had been in more limited use in BrE for a long time before that started,
of course, by British people in India.
OED:
3.
a. orig. S. Asian or in South Asian context: sure, certain,
reliable; genuine, bona fide, correct. Hence more generally: real,
not sham; (of information) factually correct; (of persons)
authentic, not pretended; proper or correct in behaviour, socially
acceptable (cf. echt adj.).
1776 Trial Maha Rajah Nundocomar for Forgery 102/1 Maha Rajah
said it was necessary to witness it to make it pukka.
1857 Ld. Lawrence in R. B. Smith Life Ld. Lawrence (1883) II. i.
11 Your Lahore men have done nobly... Donald, Roberts, Mac, and
Dick are all of them, pucca trumps.
1858 Col. Keith Young in Diary & Corr. (1902) App. D. 329 On
receiving pucka information..that the Insurgents were at Singpore.
1893 G. Allen Scallywag I. 44 That's a good word... Is it pucker
English, I wonder.
1919 J. Buchan Mr. Standfast i. v. 113 My boy's at home,
convalescing, and if he says you're pukka, I'll ask your pardon.
1924 E. M. Forster Passage to India i. iii. 26 Mrs.
Turton..remarked that Mr. Fielding wasn't pukka, and had better
marry Miss Quested, for she wasn't pukka.
1948 Observer 25 Apr. 2/1 Produced for the Government of
Southern Rhodesia, that forty minute film..is one of many from
British studios that are being specially commissioned to give
straightforward information on important subjects—in fact ‘pukka
gen’.
1967 R. Singha & R. Massey Indian Dances xviii. 157 These
barracks once the epitome of pukka British army tradition, for
many years echoed all day to the sounds and rhythms of Indian
music.
1976 Physics Bull. Nov. 480/1 What it does show is a pucka trade
union doing a proper trade union job.
2006 Times (Nexis) 6 Mar. 20 Adopting her own pukka English
tones.
b. Brit. slang. Excellent, superb; ‘cool’.
1991 Sun 13 June 23/6 Hey, man, that shirt's pukka.
1996 Observer 5 May (Review Suppl.) 7/6 Girls mug girls for
jewellery or pukka clothes.
2002 C. Newland Snakeskin xix. 255 ‘Yuh mum's pukka,’ Davey
chimed in, with so much passion I knew he wasn't just being
polite.