Ever wondered where your Amazon delivery comes from?

It's big. Very big. About 700,000 sq ft, says Gary Norton. The size of 10 football pitches adds Neil Williams. Or to put it another way, about the size of a dozen large out-of-town supermarkets.

If ever you needed an example of how the internet has changed consumer habits, the vast Amazon Fulfilment Centre at Rugeley – that's a warehouse to the rest of us – is surely it.

The company is coy about the precise figures, but every day hundreds of thousands of items will arrive in one end of the building, and every day hundreds of thousands will be dispatched from the other.

At peak times, it is believed that the centre will process 35 items a second.

And it is all in the barcodes, says site leader Gary, who took over responsibility for the centre last month. It is the barcodes which enable each item to picked out from the millions of others lining the vast shelves, the barcodes which match the products with the customers, and the barcodes which identify where each package should be delivered.

The warehouse, which opened on the site of the former Lea Hall Colliery in 2011, is now Rugeley's biggest employer.

It has a total of 1,000 permanent workers plus 400-500 who work on a casual basis, although the number is considerably more at peak times such as Christmas.

"We can reach 2,000 workers at busy times," says Neil.

Gary, a 45-year-old father-of-three from Burton upon Trent, joined Amazon in September, 2015, and has worked at both the Rugeley centre and an even larger one at Coalville in Leicestershire.

Before joining the company, he has performed similar roles at the Co-op, Rolls-Royce, train manufacturer Bombardier, and as operations manager at Molson Coors brewery in Burton. If that has not kept him busy enough, in his spare time he is a director of Gresley FC, having served two stints as the club's manager.

"My 19-year-old daughter at university loves the fact that I work at Amazon, she's constantly texting me, asking for stuff she wants," he says. "My other kids think it is pretty cool, too."

But while the company has similar centres across the country, Rugeley is a national, not a regional centre. Goods leaving the site could easily be bound for Scotland or the south of England, and just because a customer lives in Cannock or Cosford, it doesn't automatically follow that it will come from Rugeley.

It depends more on the nature of the product, rather than the location of the customer, says Gary.

"Coalville tends to specialise in the large items, whereas here we focus on the smaller ones," he says. "The highly scientific measurement we use is if they are larger than a Monopoly board, they will be at Coalville, if they are smaller we will have them here."

An ever-changing system of algorithms ensure that everything runs with laser-like precision.

"The algorithms are amazing," says Gary.

"When you place an order, they will work out where is the cheapest and quickest location that has the item, which is best for the environment.

"It might be that one of the centres is on one our existing routes, so it will make sense to send it from there."

It is this precision which has enabled Amazon to introduce a same-day delivery service, meaning that in some locations an item ordered before midday will be on your doorstep between 6pm and 10pm. But it also means that everything has to run like clockwork, and Gary is the man who has to make sure this happens.

"I have got the easy job," he says. "We have a great bunch of staff, and it is they who make it all happen.

The biggest headache can be if there is a mechanical breakdown.

"Because of the sheer volume of orders we handle, if one of the conveyances breaks down, even for a few minutes, it can have a huge knock-on effect," he says.

The majority of goods on sale – 55 per cent – come from external suppliers, and the sellers are required to attach their own barcodes to a very exacting standard before they arrive at the depot.

"If a barcode was wrong, it would cause very serious problems, but it never happens," says Gary.

"I can't explain why, but it just doesn't happen."

But if you think the millions of different items are meticulously filed in easy-to-find locations, you are in for a surprise.

To prove the point, community relations manager Neil Williams pulls out a packet of wool and an Egyptian musk incense set, which are located next to one another.

Gary adds: "We have prime spots, close to the conveyors, and we will tend to put the fast-moving items there, and the slower moving ones at the back.

"But otherwise it's pretty random. If, for example there was a new film released, and there was a big rush of orders, you wouldn't want them all in the same place, as it would get very crowded around there."

It also makes sense to have the big-selling items dotted all over the centre, so that the 'pickers' who are responsible for picking up the items are never too far away.

But given the random way the goods are distributed, how do the pickers find them? Again, it is all in the barcodes. Avril John, 67, from Rugeley, enjoys working as both a 'receiver', who stows the items on the shelves, and a picker who takes them off. For both duties she will carry a hand-held scanner, which stores and records the crucial data that ensures everything runs smoothly.

"When I'm on receive, the stuff comes into the dock for unloading," she says. The hand-held device will then identify suitable locations for storage, and provide the appropriate directions, and once it is in place she will scan the barcode which will feed the information into the database.

Then, when a customer orders the item, the picker will receive a message directing them to fetch the goods from the appropriate location.

As they work their way through the list of goods to collect, they will drop them in a black box – known as a tote – which also has its own unique barcode. Once the box is full, the picker will put it on one of the numerous conveyor belts which wind their way around the centre.

Amazon is unable to say how far the conveyor belts stretch, but it is thought to be about nine miles, and they are designed so that a picker is never too far away from one. And whichever one the picker uses, the destination is the same – the packing area.

It is here that the goods arriving on the conveyor belt are sorted, being separated for each customer, who will have been assigned a pigeon-hole in a mobile 'customer wall'. Again, this is done by scanning the barcode, with the hand-held gun telling the staff in which pigeon-hole to put the item.

Dave Wasiuk, 55, from Stafford, is a retired RAF sergeant who now works as part of the packing team. He invites me to help him putting the orders in their packaging ready to be sent out.

"I like the sense of camaraderie," says Dave, who has been at Amazon for four years. "It's a bit like being in the RAF in that respect, you work as a team."

He hands me my first order to process, a small electronic device. Scanning the barcode on the item tells me it needs to be packed in an A1 envelope, which is in a rack on the desk. Once the item has been parcelled up, it is time to scan a second barcode on the outside of the package, before putting it back on the conveyor.

The next stage of the process is the labelling, and it is perhaps this which is the most technically impressive. A machine known as Slam – scan, label, apply, manifest – scans the barcode as it makes its way along the conveyor, processes the information, and then prints and applies the name and address of the customer. This takes place all within the time it takes for the parcel to move about six foot along the conveyor – probably no more than four or five seconds. Even more impressive is that the machine which applies the label never actually touches the parcel.

"It blows the label onto the package so that it doesn't damage it," says Neil. "It then weighs the item, to check there is the right amount of packaging in it, and if it is not the correct weight it pushes it off the conveyance so we can take a look at it."

The final stage sees the items mechanically sorted for their final destination. Once more, the barcodes will be scanned, so they are sent down the appropriate chute for their geographical location.

Gary says one of the things he enjoys about the job is joining the staff on the different lines, and says he often finds himself having competitions with them to see who can do their jobs the most quickly.

Most of the staff are trained in all aspects of the process, which allows both for greater flexibility in how they are deployed, although Gary says some workers do prefer to focus on particular jobs.

"Some people like the picking, as it gives them a good workout," he says. "I would be guessing, but I imagine they walk eight to 10km a day. The important thing is to wear sensible shoes," he says.

Earlier this year, Amazon overtook Microsoft to become the world's biggest company, and one can only see the company going in one direction. This is truly a place of Amazonian proportions.