Workers in any job in Scotland only get premium rates if that has been put in their contract by their employer. Wage rates have nothing to do with the Scottish government, although hours of trading are their responsibility.
Many of the large retailers have reduced or removed premium rates uk-wide, so that they can afford to pay the new minimum living wage. (That is the reason they give.)
In Tesco, of which I have personal experience, as gillybob wanted, most UK workers are paid 1.5x their hourly rate for Sunday work. Some long-serving workers are still entitled to 2x their hourly rate, however Tesco has recently told them that this right is to be removed, after payment of a lump sum as compensation.
Many Tesco workers and, seemingly, the union Usdaw believe that if Sunday trading hours are extended in England and Wales, the large retailers will do away with premium rates altogether in order to afford the increased number of hours.
That would affect far more people in England and Wales than in Scotland, simply because of the relative population figures.