^I know you said it depends on where you. But you then go onto say in the EU it's the stores problem and that it is not Illegal to buy if you are under age. But as the UK is part of the EU it is most certainly an offense
http://www.cps.gov.uk/legal/l_to_o/licensing_of_alcohol/
It's in the section Purchase and consumption of Alcohol by Children,
A child under 18 commits an offence under section 149 if he buys, or attempts to buy alcohol, unless that act is committed in the course of him being used for a test purchase operation (Stone's 8-19829ZC).
A person who acts as an agent for a child under 18 by buying, or attempting to buy alcohol on behalf of the child also commits an offence, as does a person who acts as agent for a child under 18 and buys or attempts to buy alcohol for him for consumption on relevant premises.
However, this last offence does not apply if:
- the person purchasing or attempting to purchase the alcohol is over 18
- the child is 16 or 17
- the alcohol is beer, wine or cider
- the purchase is for consumption at a table meal
- the child is accompanied by an adult.
A person guilty of an offence under this section is liable on summary conviction:
- in the case of an offence committed by a child under 18, to a fine not exceeding level 3 (£1,000) on the standard scale.
- In the case of an offence committed by a person acting as an agent for a child under 18, to a fine not exceeding level 5 (£5,000) on the standard scale.
A child also commits an offence under section 150 if he knowingly consumes alcohol on relevant premises, and a person to whom section 150(3) applies commits an offence if he knowingly allows the consumption of alcohol by a child under 18 on relevant premises.
A person guilty of an offence under this section is liable on summary conviction:
- in the case of an offence committed by a child under 18, to a fine not exceeding level 3 (£1,000) on the standard scale.
- In the case of an offence committed by a person who knowingly allows the consumption of alcohol on relevant premises, to a fine not exceeding level 5 (£5,000) on the standard scale.