News that the Scottish Parliament will debate plans to ban under-21s from buying alcohol in off-licences has been warmly welcomed by the Coalition Against Raising the Drinking Age in Scotland (CARDAS).

The Scottish Government proposal – which it says is backed by the results of pilot schemes in various locations – has been seriously criticised by opposition parties and student groups since it was put forward.

CARDAS is engaged in lobbying MSPs ahead of this Thursday's vote, which itself cannot force a change in Government policy. However, the campaign group is confident a defeat would put serious pressure on the SNP.

"We very much welcome moves to force an open and honest debate in the Scottish Parliament on this daft and discriminatory proposal," CARDAS coordinator Tom French said.

"With such a wealth of evidence now clearly highlighting that raising the minimum purchase age will not help tackle alcohol misuse in Scotland it is about time that the Scottish Government faced the music and allowed these plans to be openly scrutinised so they can be seen for what they are.

"I am certain that MSPs will have the sense to vote down these plans and instead put forward evidence-based solutions to the alcohol problem."

Conservative young people spokesperson Murdo Fraser, who will lead the debate, called for the other opposition parties to stand together against the plan.

"We will be making a bid in the Scottish Parliament to get a clear statement of parliamentary intent on the SNP's plans and we are confident this will have cross-party support. Scottish Conservatives were the first party to come out and oppose the half-baked plan to raise the age for purchasing alcohol in off-sales from 18 to 21.

"Since then, we have seen many others follow suit, including the SNP's student wing. If the SNP were unable to persuade even their own normally ultra-loyal student activists to support this ludicrous policy, there is not the slightest prospect of them being able to persuade the rest of the country," he argued.

Other opponents have questioned the pilots, arguing that other initiatives such as increased policing may have had a greater impact on reducing crime and disturbances. The Scottish Government, however, has firmly backed the trial results.