Tea production started in Sri Lanka in 1867 by the British. 33 years after it was started in India. The British (private) owners ran the estates until independence in 1948. In 1948, all tea estates run by the British were nationalised and most of the British (who had basically been living like kings) had to go home.
For the plantations up in the central high country, they are now operated by private companies, on top of government owned land. The government used to manufacture all the tea in Sri Lanka but by the 1980’s they had labour issues and so privatised the plantations. Now they only collect the rates and taxes.
However, the black tea industry in Sri Lanka remains highly regulated. This is to ensure that standards are maintained so that you can be sure you get quality Ceylon tea and that prices remain fair to all parties concerned. The system is designed so that nobody can undercut anybody else by unfair practices.
Non-black tea is unregulated. So a plantation producing green tea can sell it on-the-side to whoever they want to. This is because Ceylon tea is traditionally black tea. Nowadays they also produce green, white, golden tip and silver tip. Golden and silver tips are part of the black tea family but originally they were regarded as imperfections (along with impurities, twigs, dust, fibre, etc.) that had to be removed from the proper black tea.
But times change and they now produce green tea, mostly using the Japanese method of steaming. And they blend into normal black tea golden and silver tips when customers request it.