Four of the world's biggest tobacco firms have launched a High Court bid to challenge the legality of the Government's new plain packaging rules.
The rules banning the use any logos or branding on cigarette packets are due to come into force in May next year. Under the regulations:
Any part of tobacco packaging not covered by a health warning must be a dark brown or green colour.
Brand names must be in small, non-distinctive lettering.
The legal action has been taken by Philip Morris International, British American Tobacco, Imperial Tobacco and Japan Tobacco International.
They claim that the regulations violate a number of UK and EU laws, and are "disproportionate".
It is being contested by the Health Secretary Jeremy Hunt, who argues that the regulations are lawful.
Mr Justice Green will rule on the legality after a hearing which is expected to last for six days.
In 2012, Australia became the first country to pass compulsory laws for all tobacco products to be sold in plain packaging in a bid to deter smoking.
Since then, studies suggest plain packaging is working to reduce the attractiveness and appeal of tobacco products and is acting as a deterrent on smoking.
According to Australian Bureau of Statistics, total consumption of tobacco and cigarettes in the first quarter of 2014 was at the lowest level ever recorded.