What are the key arguments in the farm inheritance tax debate?

Farming is often not a lucrative business, and the work is difficult, so people often do it simply because it is the family business. Photograph: Henry Nicholls/AFP/Getty Images

Thousands of farmers plan to descend on central London on Tuesday to protest against changes to inheritance tax announced in the budget last month. The farmers argue the changes will destroy family farms, while the government says it will make no difference to food security. But who is right?

What are the tax changes?