Possible Clues:

• Secures rent for one of a group of shops
• National retail outlet
• Linked outlet that sells tea, not online?
• Cashier not working for retail enterprise
• Cashier not working in shop
• Eton's a rich organisation for such an outlet
• Outlet keeping tea in reserve
• Retailer with stocks of tea
• It's a job keeping one institution as a high street enterprise
• Woolworth's was one