The Scottish Conservatives are sending out 10,000 postcards to 18-year-olds in marginal constituencies, encouraging them to oppose Scottish Government plans to raise the legal age for alcohol off-sales.

The move follows a non-binding vote in the Scottish Parliament last week, in which the Government's move to increase the legal age for buying alcohol in an off-licence from 18 to 21 was rejected.

Opponents of the move, which the Scottish Government says was proven to reduce alcohol-related crime and disturbances in pilot schemes, include the Holyrood opposition parties, the National Union of Students and members of the SNP's student association.

"Despite the comprehensive defeat it suffered on Thursday, the SNP Government is still determined to press ahead in some form with the criminalisation of those under the age of 21 who want to purchase alcohol from off-sales," said Murdo Fraser, Scottish Conservative deputy leader.

"The Scottish Conservatives want to see a mature and reasoned debate around Scotland's relationship with alcohol. It is our view, a view now endorsed by the Scottish Parliament, that the Scottish Government's proposals are ludicrous, discriminatory and not addressing the fundamental issue.

"Every 18-year-old deserves to know what the SNP thinks of them, which is why we are sending this message out today," he added.

Labour's leader in Scotland, Iain Gray, last week dismissed the proposal as "daft", questioning the sense in allowing 18-year-olds to work in off-licences and drink in pubs, but not buy alcohol from off-licences.

He instead called for a "mandatory" scheme to require proof of age for off-sales, and tougher sanctions on businesses found selling to underage young people. Gray also signalled he would be happy to discuss minimum pricing, although some legal experts believe this additional measure is in conflict with EU and UK competition laws.