Supermarket delivery services gear up for a bumper Christmas

Fifteen miles of conveyor belts, 3.7 million packets of stuffing and thousands of 'pickers'...more and more of us do the biggest shop of the year online.

This week, there is a good chance that you or I have done some shopping, online. The end of the first full week of December represents the single busiest moment of the virtual season. Busiest, though by no means the first. Waitrose has been fielding festive orders for weeks. So many, in fact, that its delivery schedule for the 23rd – the final day of delivery, for everyone who doesn't live in Acton, west London – is almost full up.

Similarly at Tesco, where slots in the week before Christmas are more sought after than invitations to the royal wedding. At Sainsbury's it's the same story. And then, of course, there's Ocado, for whom Christmas represents the climax of the year. Come December, its warehouse in Hatfield, Hertfordshire, becomes a hive of activity, as shoppers turn to the site to cope with the challenge of buying in bulk.

Want one of its Christmas Eve slots and you'd best book in October. This year, it expects to send 40,000 Christmas puddings, more than a million mince pies and 35 million calories worth of brandy butter zipping around the country.

"We started planning our Christmas operation this time last year," says Lawrence Hene, head of grocery retail. "Expectations are raised when it comes to it. If I turn up on the 24th without your turkey, it's not going to be OK." That's one reason why it offers to send out emergency vans – complete with snow tyres and tracking devices – should anything go awry.

At Tesco, the figures are even more eye-watering. Over the next few weeks, it expect to sell a staggering (and slightly nauseating) 2,200 tons of turkey, 3,200 tons of sprouts and 3.7 million packets of sausage meat and stuffing. Chocolate coins? Two million packs. Clementines? One million nets. Given that last year saw roughly £45m worth of its business being done online, that adds up to an awful lot of food flying through cyberspace. Festive shoppers, says the supermarket, tend to be older than its usual online market: families, keen to avoid lugging the masses of mince pies through the car park.

They also shop differently. Unsurprisingly, booze is a big hit with the Christmas customer – Waitrose sees quadruple the rest of the year's online wine orders in the run-up, and isanticipating that half a million bottles of wine and champagne will fly off the virtual shelves.

It sees party food – cakes, platters, meat selections – increase by more than 1,000 per cent, with hampers trading at 40 times their usual rate. The online Christmas boom is big business for retailers. But it's also a mammoth piece of organisation.

By and large, when a customer places an order, the store closest to them is notified. Dedicated "pickers" or "personal shoppers" are deployed to select customers' products from the aisles, scan them, and get them ready for delivery. Most of the time, they are shopping for several different customers at once, using super-sized trollies paired with computers telling them who wants what.

Much power lies with these pickers: it is with their choice that your biscuits crumble or stay intact, that your apples bruise or remain rosy. If you have allowed substitutions to be made, they are instructed as to other suitable alternatives by the scanner. Come Christmas, pickers are in high demand; it's not unusual to see a boom in short-term employment as their services are required.

But if this sounds impressive, then the new generation of "dotcom" stores sound positively futuristic. With the launch of its own delivery system inside the M25 (previously all London deliveries were dispatched via Ocado), Waitrose has opened its first online-only store (or "dotcom fulfilment centre") in Acton.

At 37,000 sq ft, it is laid out just like a high street branch of the supermarket only, instead of customers, it is packed with several hundred pickers – the centre's launch saw some 1,200 jobs created in the capital. Tesco operates a similar system, with dotcom stores in Greenford, Aylesford and Croydon. When the next one opens, in Enfield, their reach will be extended even further

But it's at the Ocado warehouse where things get really innovative. The website allows customers to choose from across the board: virtually every brand imaginable, as well as some of its own and Waitrose's home brands, are available. Without the local stores to accommodate a picking system, Ocado's warehouse has taken on an almost cult-like status among consumers.

At 300,000 sq ft, it is the size of ten film lots and processes the equivalent of 30 supermarkets' worth of sales. There are 15 miles of conveyor belts within the building, which carry the so-called delivery "totes" from one station to the next, their paths determined by an intricate system of computers. The secret is the company's IT system, worked on by some 150 programmers.

At each station, items are picked manually or mechanically; either way, the computers have programmed the bag's journey around the conveyor belts so that, when packed, fragile items will be protected. On a busy day, that means about 16 picks every second.

And it's a trend that shows no sign of slowing down. Tesco has seen consistent double-digit grown online for more than a decade, and Waitrose is already declaring this its "biggest online Christmas yet".

Next year, Ocado won't have just the one hi-tech warehouse; the company is spending £80m on a new one near Tamworth in Warwickshire, and creating 2,000 jobs in the process. "It's only going to get bigger," agrees Hene. With increasing numbers of us heading online, super-sized "dotcom fulfilment centres" are only going to become a more familiar feature on the consumer landscape.