Amazon uncovered: behind the scenes at one of its biggest UK warehouses

Ever wondered what happens between ordering online and finding the parcel on your doorstep the next day? 

With Black Friday sales in full swing, Which? went behind the scenes at one of Amazon UK's biggest fulfilment centres to find out more.

From conveyor belts whizzing overhead to robots moving shelves along 'super-highways', it's a far cry from a traditional warehouse. 

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What happens at an Amazon fulfillment centre?

Amazon's super-sized warehouse in Dartford processes hundreds of thousands of orders a day. 

The four-floor warehouse, built on the site of a decommissioned power station right next to the Dartford crossing, is vast. It has the footprint of six-and-a-half football pitches - that's more than two million square feet of operating space. It's so big staff are given bicycles to get around more quickly. 

Bikes at the Amazon warehouse

The building is known as LCY3 after the nearby London City Airport.

In fact, most Amazon fulfilment centres are named with the codes of nearby airports - BHX for those near Birmingham, LTN for those near Luton and so on. 

The Dartford centre opened in August 2021 and is fitted out with all the very latest technology. There are even 8,000 solar panels on the roof. 

It's one of 32 similar fulfilment centres across the country. When you order from Amazon, your delivery could come from any one of these centres - although algorithms predicting who will order which items and when means it's likely your order will come from one of the centres closest to you.

The centre in Dartford, for example, tends to serve a radius of about 20 to 30 miles. 

Amazon opened its first UK fulfilment centre in Marston Gate, Milton Keynes, in 1998.

Meet the Amazon robots behind your delivery

The secret behind Amazon's ultra-efficient delivery model is its army of 2,000 robots. You can see the blue robots under the shelves in the picture below.

Robots moving shelves at Amazon Moving at 4mph along warehouse corridors known as 'super-highways', they use hydraulic rams to lift vertical shelving units up from beneath and whisk them off to the outer reaches of the warehouse. 

The robots move in 90-degree angles, using unique barcodes on the floor to help them navigate. And they're clever: they can automatically avoid fallen items on the floor and send alerts to engineers.

They also know when they're running out of battery and take it upon themselves to go and find a charging dock every hour or so to boost their power. 

How the robots maximise storage space

From babies' nappies to bike lights and air fresheners, a peek inside the storage units is a reminder of the vast range of the weird, wonderful and simply mundane items sold by Amazon.

The warehouse stores millions of items on these vertical storage units, known as pods.

There are also thousands more whizzing overhead at any one time on 13km of conveyor belts - either on their way in or out of the warehouse. Workers pack each item into the pods, before robots whisk them off to be stored in the outer reaches of the building.

The pods are positioned with just a 15-20cm gap between them to make the most efficient use of space. This means Amazon can store up to 50% more items as it doesn't need to allow room for traditional access aisles. 

How are Amazon orders packed? 

Packing is pretty high-tech too.

Amazon associates scan each item before a computer tells them which box is the best size. Machines then spit out a pre-cut pieces of sticky tape exactly the right length. They also print sticky barcodes containing order details and the customer's name and address. 

Amazon associate selecting packaging

Another conveyor belt directs packages off to the final stage, where they're weighed to check they contain the right item - and only the right item. (If not, they're kicked off the conveyor belt to be checked manually).

Then an address label is fixed on by a machine using air pressure.

Finally, the parcels are sent down a chute on their way to customers.  

Conveyor belt at Amazon On the ground floor is the nerve centre of the building, known as 'Flow'. Here, workers in hi-viz jackets monitor a bank of enormous screens to check everything is working as it should across the building. 

Some 2,000 people work in the fulfilment centre, on wages starting at GBP11.45 an hour. The warehouse is open 24 hours a day with two shifts of 10 hours.

Workers typically do four days on and three days off. 

And it's not just pickers and packers, there are 60 different roles in the building including technicians for the robots and a number of highly skilled engineers. They all get an employee discount of 10% on items sold by Amazon. 

Amazon directly employs 75,000 staff in the UK.

The secret code on your Amazon label

Did you know there are secret codes on your Amazon labels? 

If you've ever wondered where your specific delivery has come from, you can use the codes - usually based on nearby airport names - to help you figure out its journey across the UK to your doormat. 

Amazon label with codes

Here you can see this parcel was picked and packed at Peterborough (code EUK5), sorted at Redditch (code BHX8) and then sent to Oxford (OX2) for delivery.

Why your box is picked by a machine 

We've all heard stories of online deliveries in ridiculously large boxes. So how does that happen?

All the items entering Amazon fulfilment centres for the first time go through cubiscan - a three-dimensional laser scanner which measures the dimensions and weight of each product. This feeds into software which can then recommend the optimal box size for each item.

So how does it sometimes go so wrong? Usually because it's measured incorrectly to start with.

Amazon says it rescans any item reported as having been delivered in the wrong size box.

What else should I know when shopping with Amazon?

Multiple Which? investigations have revealed the widespread presence of fake reviews on online marketplaces, including Amazon. Sometimes sellers pay genuine customers to place good reviews, skewing a product's star rating in order to make more sales. Sometimes reviewers didn't even buy the product, and they've just been paid to write reviews.

Read our full guide on how to spot a fake review for more.

You might also not realise that Amazon isn't responsible for the safety of all the products sold through its online marketplace. Earlier this year, we put 11 cheap baby carriers and slings bought from Aliexpress, Amazon or eBay through British safety standard tests. Ten had at least one serious failure and nine could be potentially lethal if used to carry a real baby.

And last year, a Which? investigation found teeth whitening products with illegal levels of hydrogen peroxide for sale on Amazon Marketplace.

Which? is calling on tech firms to do more to end the sale of dangerous products online

Finally, every year we survey thousands of people on their experiences shopping in-store and online to help us find the best and worst places to shop for clothes, entertainment, furniture, homeware, DIY, beauty, and baby and child.

The results include Amazon, along with traditional bricks-and-mortar stores. 

Read our full best and worst shops guides to see how customers rated Amazon in different categories.