Hi N2016
ESA is awarded on an indefinite basis, but people can be reassessed after one, two or three years. Yes, some people have had much longer gaps, but that is because the DWP has been behind with reassessments. So you look as if yours has just come around after three years. Unless your last letter specifically states that you should not be reassessed for a particular length of time, or not be reassessed at all, you will have to complete the form.
BIS
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