Even Father Christmas was present, having taken a day's break from his North Pole workshop to welcome shoppers and make a few purchases of his own.
Geraldine James, Selfridges Christmas Home & Decorations Buyer, said: "Despite the summer weather, we're in full festive mode here at Selfridges. We've been working on this year's Christmas Shop since Christmas last year.
"We have so many customers visiting from all over the world and eager to snap up festive souvenirs on their summer holidays, which they can't buy at home.
"So, we have to make sure we're ready to showcase Christmas decorations they will truly treasure."
For shoppers who like to plan ahead, trends for Christmas 2015 include personalised decorations, black and white monochrome and 'Magical Forest', which includes wood-based decorations and woodland creatures.
The store also revealed that this year's Christmas theme is 'Journey to the Stars', with a special line of decorations called 'Moonlight Magic' launched today.
The shop's very first customers, Holly and Ken Martin, from Pennsylvania, USA, bought a Christmas 2015 bauble to mark their UK holiday.
Each of the thousands of Selfridges glass baubles was designed exclusively for the store and was individually mouth-blown from one carefully-selected supplier in Hungary.
The second phase of the shop's opening will be in Autumn, when the floor space devoted to all things festive will be more than doubled to 60,000 square feet.
Open fully, the winter wonderland will include more than 60,000 baubles, 120+ cracker options, and 1,250+ different cards and wrapping paper designs.
But for now, it's all hands on deck – especially for the man in charge.
When asked if he shouldn't be taking it easy in August, the man with the beard said: "Relaxing? Oh I'm afraid not.
"Christmas is all year round – I do take a little break in January but now is build up time, getting ready for the big day."
Budget Christmas presents for family and friends
Selfridges has already launched its Christmas shop
Is your man the back-to-nature type? This firestick from Hunter Gatherer will mean he can dump the lighter. Just strike the blade down the firestick, and a shower of sparks will start his camp fire - with a bit of patience and the right kindling, that is. It costs £14 from Not On The High Street; and for another £16 you could add a chestnut roasting pan for a romantic evening by the fire.
From Not On The High Street comes this selection of four of the world's hottest chilli powders - including the current world champion, Scorpion Moruga. Each comes in a tiny corked glass bottle, all contained in a standard sized matchbox. The quantities may be tiny - but with this level of heat, that's all you'll need. £6.
So you can't stretch to a day at a luxury spa? Never mind. These pretty lights will turn bathtime into a real pampering experience. Attach the waterproof spa lights to the side of the bath, or simply float them on the surface; add bubble bath, put on some relaxing music - and ask if there's room for two. Spa lights £6.95 from Prezzybox.
Bath bombs can cost a fortune to buy, but they're cheap and very easy to make. Just mix together three parts sodium bicarbonate, one part each of citric acid and Epsom salts and a few drops of essential oil such as rose or lavender. Add a little almond oil drop by drop until the mixture is still a bit powdery but clumps together when squeezed. Use a plastic mould to shape your bombs. Or buy a kit - Bee Beautiful's includes everything needed to make a dozen bath bombs for £19.99.
It's too late to gather your own this year, but dried lavender is widely available online. And turning it into a scented sachet or even pillow couldn't be easier. Just sew a little bag from any scrap of pretty material - vintage handkerchiefs look stunning and don't need hemming - and pop the lavender inside. It's easy to personalise the bag with a little embroidery.
From just £10, Photobox will help you create a personalised calendar with a different happy memory for each month. Just upload a dozen family photos and some captions, and the company will get the finished calendar to you in as little as four days. There are plenty of different formats to choose from.
Even a simple wooden doll's house can cost well over £100 - and that's before you've bought the furniture and the dolls themselves. But this charming two-storey castle dolls house from Tesco comes with 5 pieces of furniture & the princess' vanity set two dolls, two sets of stairs and eleven pieces of furniture for just £36.99 - even less using Clubcard Boost.
Small boys everywhere love ice cream and space, so this Astronaut Ice Cream should go down a storm. Originally developed for the Apollo space missions, it's made by the same company that still supplies NASA. Freeze dried and vacuum packed, it comes in three flavours and literally melts in the mouth. It costs £5 from the Great Gift Company.
These plastic animal toys are perfect for the little ones this Christmas. They're very durable and perfect for encouraging mobility and learning with animals sounds and music included. The set costs £19.97.
Drawn your worst enemy in the Secret Santa? Here's how to put the boot in while maintaining the moral high ground. Oxfam's gifts of goats and sheep - which of course actually go to a worthy recipient in the developing world - have been very popular in recent years. But did you know the charity also offers £9 loads of manure for farmers? Just hand over the gift card to the recipient, and smirk.