Inside the warehouses that make a shopping festival possible

The first thing you notice is the sound: tape guns, conveyor rollers and the beep of scanners, all at once and without pause. The second is how few people it takes. A hall the size of a football pitch is staffed by a few dozen packers, each handling several hundred parcels an hour.

The peak is built months ahead. Forecasts are broken down by product line and postcode, temporary staff are hired and trained in August, and popular items are pre-positioned in regional depots so that a next-day promise can be kept.

The economics are brutal but simple. Margins on the festival's discounts are thin; the profit comes from customers who stay. That is why the return process is as carefully designed as the outbound one.