A senior Labour figure at Westminster has ridiculed the idea of an autonomous leader of the party in Scotland as "entirely impractical".

Joining the debate started by former Holyrood Minister Tom McCabe, an article in The Herald today by Tom Harris argues the counter view. The Glasgow South MP claims: "Creating a new post of leader of the Scottish Labour Party would be so fraught with difficulties as to make it entirely impractical.

"Under such an arrangement, Labour MPs at Westminster would owe allegiance not to the Prime Minister but to the Scottish leader, and would, presumably, be mandated to support policies on reserved matters that were developed, not on a UK basis, but entirely in Scotland."

The Westminster Transport Minister adds: "This may have some superficial attractions to those of a nationalist bent, but it runs entirely at odds with the Scotland Act and to the 1997 White Paper which stated explicitly: There are many matters which can be more effectively and beneficially handled on a United Kingdom basis'."

Mr Harris also asks: "Is Tom really arguing that Labour would have been more successful in Scotland had Henry McLeish, and not Tony Blair, been leader? Or that Donald Dewar lacked authority because he was technically only the leader of the Scottish group of Labour MSPs?"

All three candidates as leaders have endorsed to some degree the notion that the job of Holyrood leader of Labour has to be enhanced beyond that of being a mere parliamentary group leader.

But yesterday one of Labour's most eloquent critics of devolution, former Minister Brian Wilson, told some of his party colleagues north and south of the border some brutal truths.

Describing the three candidates for Labour leadership as "scarcely inspirational" and incapable of laying a glove on Alex Salmond, he claims the "devolution is now irreversible" and his party must respond.

"Much will depend on the new Holyrood leader who must have fresh ideas and be able to articulate them with clarity, but also match Salmond blow for blow on setpiece occasions.

"That leader should have freedom of manoeuvre to develop priorities tailored to Scotland's needs. It is ironic that devolution's strongest proponents in Whitehall are also the most reluctant to devolve power within Labour itself."

Iain Gray, the former enterprise minister, yesterday called for people to have to show a proof-of-age card to buy alcohol, claiming this would help curb under-age drinking.

He said he did not support Scottish Government plans to increase the age limit for buying drink in off-sales from 18 to 21.

Mr Gray, who is up against former health minister Andy Kerr and former justice minister Cathy Jamieson to succeed Wendy Alexander as Labour Holyrood leader, claimed these proposals were "unworkable and unfair".

He suggested: "I believe that a mandatory proof-of-age card for buying alcohol would be a much more effective and much fairer way to tackle under-age drinking, rather than a blanket increase in the age limit.

"It would also help protect retail workers who have to make difficult judgments about age and face disciplinary action or even the sack if they get it wrong."

The East Lothian MSP said ideas such as that showed he was "the new voice with the fresh approach and the right ideas to take Scottish Labour forward and to take the fight to the SNP".

Mr Gray said: "The SNP have proposed an unworkable and unfair increase to the age limit for buying alcohol. It does not make sense to justify preventing 18 to 21-year-olds from drinking responsibly by saying it will reduce teenage drinking.

"The SNP should focus on properly enforcing the law we currently have."