Checking the Age of Online Purchasers

There is a private member’s bill before the House of Lords in Britain — Online Purchasing of Goods and Services (Age Verification) Bill [HL] 2008-09 — to require online retailers to verify the age of people buying goods whose purchase is restricted by age, e.g. liquor or cigarettes. It is described here.

Some scepticism has been expressed about its desirability, in part based on the difficulty of actually doing what the law would require.

Do you think this kind of law would be a good idea here? Or should we accept as a fact that age restrictions on purchases simply cannot be enforced online? Would it matter if the sellers of such goods were licensed? Is there something that could be done at the delivery stage?

Should lawmakers or protectors of youth be lying awake at night about this problem?