It has nothing to do with a drop in income, trust me.
They have given their conditions and they don't mention income.
The lack of any specific, measurable reductions in income is intentional. The taxpayer should keep evidence of the impact on their trade, but there is no link between the amount of the grant and the financial loss.
From the Institute of Chartered Accountants in England and Wales.
But you need to be 'adversely affected'.