Did British chef Jamie Oliver redefine “pukka” in 1999?

According to Collins Dictionary, since the early 2000s there has been a steady decline in the usage of pukka in printed literature. Unfortunately, it's unknown if the data includes websites, online magazines and forums, but I suspect it doesn't. Taken at face value, it suggests that the term is falling out of favour particularly among British English native speakers.

Google Ngram seems to confirm the downward trend, in stark contrast when pukka reached its peak of popularity in 1945, long before its modern slang meaning.

According to Josephine Livingstone, who was writing for Prospect in 2013; the slang form, "excellent" and "first-rate", was first recorded in 1991.

For a full biography of this tricky little word, specifically in its incarnation as a loan-word into English, there is no better place to look than Hobson-Jobson. So, what’s the true definition of “pukka”? Well, firstly, the present-day British English slang use of “pukka” is a true definition. People all over Britain use the word, all the time, to mean solid, trustworthy, sure. Observe definition 3.b in the OED’s entry:

• 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.

The article continues...

So, from Hobson-Jobson we learn that British pukka is a fairly literal loan from Hindi and Urdu (pakka), but that the English adopted it as a metaphor. Its literal sense survives in Indian terms like “pucca housing,” often used today to describe permanent residences which are less susceptible to natural disaster. [...] Hobson-Jobson reveals some of its cultural bias, however, in what it leaves out. There is no entry, for example, for pukka-sahib [see Wikipedia]. This term literally means a high-class European; a European might describe his friend thus if he wanted to suggest that he was a first-class gent. As we can read in EM Forster’s A Passage to India, however, pukka-sahib is also used satirically to refer to an attitude of prim, arrogant, magisterial aloofness: the ruling hypocrite’s pose. Henry Yule was a pukka-sahib for the ages.

Not living in the UK, and not having heard or met up with pukka I cannot say if the slang is commonly used among Londoners today, I imagine it's very familiar among the over 65s, and among youngsters who were growing up between the late 1980s and 90s. It would be lovely to hear somebody's first-hand experience.

From A Comparative Dictionary of the Indo-Aryan Languages

Pucca or pukka comes from Hindi pakka, "cooked, ripe," from Sanskrit pakva-, from pacati, "he cooks."

Pukka therefore means cooked, ripe, matured etc. in that sense.

Pukka may also mean solid, permanent, confirmed in Hindi just like concrete is used for that purpose in English, as in "I have concrete proof".

It is also the opposite of kutcha - crude, imperfect, or temporary. Kutcha has similar roots. Kutcha means raw, unripe.

See pukka vs kutcha housing:

Pucca houses are strong houses. They are made up of wood, bricks, cement, iron rods and steel. Flats and bungalows are pucca houses. Such houses are called permanent houses.

Kutcha houses are made up of wood, mud, straw and dry leaves. A hut is a kutcha house. Some people live at one place for a very short time. They build houses that can be moved from one place to another. Such houses are called temporary houses.

When did its slang sense, i.e. excellent, first-rate, first appear?

It had that sort of usage in Hindi for a very long time, but I have no links to show here. The British borrowed it from Hindi during their rule in India (1858 to 1947).

Is pukka known only in the UK? How common is it?

Not sure about its popularity in the UK, but I'm sure its common in India and among Indian English speakers. So wherever these Indians go, these words go with them.

Googling online it seems that pukka is mostly in connection with food, or is it a false impression? Can anything be really really pukka?

Of course, that's the main idea of pukka. "Khana pakaana" means to cook food. "Khana pakaao" is like [please] cook food.

As a young Brit (early twenties), I have never used pukka to mean anything unless it was making fun of or doing an impersonation of Jamie Oliver, or telling someone the name of a pie.