The A151 was originally designated such in 1921. Then, the roads were much as they had been forty or fifty years before, under the turnpike trusts. Since the Second World War, there has been much building of by-passes and the like so that the precise lines have sometimes changed but they are still fundamentally the same. The main difference in the present case is that the road designation has been extended from the A15 at Bourne to the A1 at Colsterworth, while at the other end, the easternmost three kilometres have been replaced by a new part of the A17.