All over the shop

Perhaps it is the fact that we have a multi-party system. Perhaps people don't tell the truth to pollsters. But The Mail on Sunday's poll (here) is widely out of line with previous polls (as was The Herald's poll earlier this week - see here):

The poll, based on a survey of more than 1,000 people, shows the SNP set to return 56 MSPs to Holyrood, Labour 40, the Tories 17, the Liberal-Democrats 13 and other parties three.
It has the SNP on 40 per cent for the Holyrood constituency vote, with Labour on 28 per cent, the Tories on 15 per cent, the LibDems on 14 per cent and other parties on 3 per cent.
In the second vote, for the top-up party lists, the Nationalists are on 39 per cent, Labour on 28 per cent, the Tories on 14 per cent, the LibDems on 10 per cent, the Greens on 4 per cent, Solidarity and the SSP both on 1 per cent and others on 3 per cent.

It becomes increasingly difficult to place any reliance at all on the opinion polls. I find it hard to believe that the SNP will increase to 55 (or even 56), while the LibDems decline to 13. It's not impossible, it's just not very likely. Especially when next week's polls may be expected to tell an entirely different story.