Haggis is popularly assumed to be of Scottish origin. Today's standard recipes (involving sheep innards, oatmeal, onion and herbs) are distinctly Scottish. It is central to the Scottish celebration “Burns night” each 25th January and Robert Burns referred to it in his 1786 poem as "Great chieftain o' the puddin-race!" However this praise was for a fairly recent adoption into Scottish cuisine.

Haggis appears in English literary sources as early as the 13th century; the first known written recipes for "hagese" or "hagws of a schepe" are from English cookbooks around 1430. It became popular as a dish in England during the subsequent 300 years. By contrast, there is not even a mention of haggis in any Scottish text until the 16th century, when it appears fleetingly in a verse by William Dunbar.

Haggis did not become established as a staple food in Scotland until much later. The British agricultural revolution (17th-19th centuries) brought productivity and prosperity to England but left many Scots destitute. During the 18th century Highland Clearances thousands of Scottish tenant farmers and their families were evicted by aristocratic landowners to make way for sheep. Without land or livelihood, they had to economise. They started eating the cheapest, most nutritious food around: haggis.

So, for four centuries haggis was beloved by the English, before falling from favour in England. Why? Because it had come to be seen as Scottish and was scorned as the food of the poor.

More Info: en.wikipedia.org