This is from a site advising Agency supply teachers but it's true for all AWR qualified workers
Think I filled in a form (might not have been SSP1 which seems to be for disputes) and sent Angard a copy but it was a long time ago (Angard might have provided the form). I contacted Angard as a first move and they were OK about it. Seem to remember getting a fit note from the Doctor when I returnedhttps://neu.org.uk/advice/agency-worker-regulations
"Am I entitled to sick pay?
You are entitled to statutory sick pay (SSP) if you meet certain conditions. You must have started your assignment and your weekly earnings must exceed £116 per week. If your pay varies, your entitlement depends on your average pay over the last eight weeks
. If you qualify for SSP, your agency should make the flat rate payment for the duration of your sickness absence to a maximum of 28 weeks. SSP is not paid for the first three days that you are on sick leave. You won't be entitled to SSP if you are self-employed, if you have already had SSP for 28 weeks (and the 28 weeks ended within the last 8 weeks) or if you have received Employment and Support Allowance (ESA) in the last 12 weeks.
If your agency refuses to pay SSP, you should ask them for form SSP1 or written reasons for refusing SSP. If your agency refuses to do so, you can contact HMRC’s employees' enquiry line on 0300 200 3500. HMRC can investigate the dispute".