Resumption of a retail use - CIL liability - Public forum - Planning Advisory Service (PAS)

Does anyone have a view on the CIL liability of a resumption of a retail use in a vacant former retail unit? In accordance with CIL Regulation 40 it is not possible to discount existing floorspace in the CIL calculation unless part of the building has been in lawful use for a continuous period of at least six months within the period of three years ending on the day planning permission first permits the chargeable development. However in considering the calculation of the CIL charge, the guidance states that in cases where the existing building does not meet the 6-month lawful use requirement “parts of that building that are to be retained as part of the chargeable development can still be taken into account if the intended use matches a use that could have lawfully been carried out without requiring a new planning permission.”

Residential and retail uses (now covered by Class E) are both CIL-liable under our CIL charging scheme. In the case of a proposal for the re-use of a building for mixed use development including retail uses on the ground floor (a recommencement of retail use more than 3 years after the previous retail use ceased) and new residential uses on the upper floors, is the correct interpretation that the ground floor retail use would not be CIL-chargeable on the basis that the retail use that could have lawfully been carried out under the pre-existing new planning permission? 

Any views on this would be appreciated. 

Thanks