LONDON — A battle to find space powering the ultrafast grocery delivery boom is pushing up rents in parts of London’s commercial property sector. Companies like Getir, Gorillas and Zapp, which promise to ship essential goods to people’s doors in a matter of minutes, have swept across the U.K. capital this year. Such services rely on so-called “dark stores,” small warehouses used to prepare online grocery orders for delivery. Similar to dark kitchens in the world of food delivery, these facilities don’t serve customers in-store.... ...In West London, prime rents for small industrial units of about 20,000 square feet rose...