You need no planning permission if your pop-up stays within the unit's current use class. A shop, a café and many services all sit in Class E, so moving between them is not a change of use. A bar or a hot food takeaway sits outside every class and normally needs permission.
Ask the council's planning team for the unit's planning history before you sign anything. An earlier permission can limit opening hours or what you sell.
Take on a short-term space for a pop-up shop
Planning, your agreement with the owner, business rates and fire safety for the space itself.