A distinguished researcher brought to Scotland to tackle the nation's entrenched health problems has questioned whether raising the alcohol purchase age will make any difference.

Professor John Frank was recruited from Canada to lead a team which will help shape public health policy by ensuring ideas and schemes are rigorously tested. Asked what he thought of the Scottish Government's proposals to restrict liquor sales from supermarkets and off-licences to those over 21, he told The Herald more research was needed.

Mr Frank said: "I doubt that we have really got studies to tell us whether that will work or not. I think we might want to have some good evidence.

"I know there were pilots in a few places in Scotland, but I think we might want to have some better evidence whether it makes a difference, because it clearly doesn't shut off the tap completely it only shuts off the off-licence tap and it only shuts off people who find themselves in a three-year age group." Mr Frank, whose post is jointly funded by the chief scientist office of the Scottish Government and the Medical Research Council, added that in other countries having a higher purchase age had created a "black market" in fake ID.

However, he said it was difficult for Scotland to tackle the booze culture because the power to increase taxation on alcohol is reserved for Westminster.

The former scientific director of the Institute of Population and Public Health in Canada, who is now based at Edinburgh University, also said he wasn't ruling out the possibility the over-21 scheme could make a difference, combined with a range of other alcohol strategies.

His comments came as First Minister Alex Salmond faced claims he was "ignoring the will of parliament" by pursuing the proposal when it has been rejected by MSPs.