Found it, (in with DD's drawings, erk! Glad you got me looking for it!)
Page 11, right at the bottom.
"If your payments were more than £100 a week, enter £100 in the box for each week. For example, if you got them for 30 weeks, enter £3,000. If your payments were less than £100 a week, enter the amount you received. For example if you got £80 for £30 weeks, enter £2,400. Don't include Maternity allowance"