It depends on your contract of employment with respect to sick pay. If you are one of those fortunate souls who benefits from full pay for a certain number of weeks, and you are still within the period for which full payment is made, you should be entitled to normal pay. (In these situations the company claims back from HMRC the statutory pick entitlement you had).
If you are not entitled to full pay, but a reduced figure (say 50%), then you would get the higher of either the 50% (used as my example), or the proportion of the hours you work during phased return.
So if you were working 3 days per week, you'd get 60%.