Cigarettes must be sold in standardised green packaging with graphic warnings of the dangers of smoking from this weekend as part of new rules designed to prevent young people from taking up the habit.
All packs must contain a minimum of 20 cigarettes to make sure the packs are big enough for health warnings.
Packaging of hand-rolled tobacco must also be in the same drab green colour and pouches must contain a minimum of 30g of tobacco.
The new rules are an attempt to cut the number of smokers across the EU by 2.4 million.
Action on Smoking and Health (Ash) said getting rid of "glitzy, heavily branded tobacco packs" is the "latest in a long line of achievements by the UK".
But smokers' group Forest said the new regulations "infantilise" consumers and "treat adults like naughty children".
- Why has standardised packaging become the law?
Smoking is the number one cause of preventable early death, and 100,000 people in the UK die every year from smoking-related diseases.
Every year in the UK around 200,000 children start smoking - enough to fill 6,900 classrooms.
A review of evidence of standardised packaging carried out by the University of Stirling's Institute for Social Marketing found that standard packs are less appealing, make health warnings more effective and reduce the ability of the packaging to minimise the harms of smoking.
- Is there any evidence that standardised packaging has an effect?
Standardised packaging was introduced in Australia in December 2012, where figures from the National Drugs Strategy Household Surveys have shown that the prevalence of smoking among adults fell by 15% in the second half of 2013, from 15.1% to 12.8%.
In the UK, an independent review conducted for the Government by paediatrician Sir Cyril Chantler found it "highly likely that standardised packaging would serve to reduce the rate of children taking up smoking".
- How and when did the new law come about?
The UK was only the second country in the world to pass legislation on standardised packaging after Australia in 2012, with many others following on including France, Ireland, Hungary and Norway.
The regulations became law this time last year but companies have had 12 months to sell old stock and fully implement the changes under the directive, which was adopted in 2014 but was held up by a series of court cases testing its legality.
The tobacco industry challenged both the Tobacco Products Directive through the European Court of Justice (ECJ) and standardised packaging regulations through the UK courts.
In May last year the ECJ ruled that the directive was lawful, and days later the industry's legal challenge to standardised packaging was defeated in the UK courts.
Last month the UK Supreme Court refused the tobacco industry leave to appeal the decision any further.
The EU Tobacco Products Directive has allowed the UK to go further with its regulations to require all tobacco packaging to be uniformly green with large images showing the harmful effects of smoking.
- When will the new rules come into effect?
Standardised packaging regulations, which is a UK initiative, comes into full effect on Sunday, while the rules governing minimum pack sizes and e-cigarettes are in force from Saturday.
- What about e-cigarettes?
E-cigarettes must now be child resistant and tamper proof, tank sizes can be no more than 2ml and the nicotine strength of liquids no more than 20mg/ml.
There must be a 30% health warning on the front and back reading: "This product contains nicotine which is a highly addictive substance."