There's a myth about luxury and digital. That luxury doesn't 'do digital'. Because the web is for bargain hunters. And luxury items must sell at top whack in a bricks-and-mortar store. Preferably while quaffing champagne as pixies sprinkle gold dust on the floor.

Okay, so the last bit isn't true; but neither is the myth. If luxury and ecommerce don't mix, someone should tell Net-A-Porter and Yoox. The two luxury retailers just merged to create a business with net revenues of £900+ million a year. Even if ecommerce doesn't work for a luxury brand, digital is still relevant.

According to Google, over 90% of luxury shoppers research products and services online before they buy. And McKinsey found that the digital universe influences more than 45% of luxury purchases. "By the time many shoppers have reached a bricks-and-mortar luxury store, they're likely to have a good understanding of all the products in the category, including features and prices."

But luxury brands are neglecting the early phases of the customer journey. At last year's Luxury Interactive Conference, 62% of marketers said they wanted to drive 'trackable conversions'. Compared with 18% who prioritised driving visitors in-store. No wonder brands such as Prada, Gucci and LVMH have posted flat growth figures despite double-digit growth in the industry as a whole.

HSBC managing director, Erwan Rambourg, holds a theory that poor performance relates to some luxury brands becoming too ordinary. His recent book ranks luxury brands in a new hierarchy. At the top are ultra highend bespoke products from the likes of Bottega Veneta. At the bottom are the more available 'everyday luxuries' such as Starbucks. (I wonder if Rambourg has ever used the toilets in Starbucks? It's neither everyday nor luxury.)

My theory is that luxury brands aren't keeping up with the high expectations of digital consumers. High-income earners love high-end technology. And people who like to diamond-encrust their smartphones and small dogs tend to have high expectations generally. But luxury brands aren't meeting their digital expectations. Take WiFi, which many of us now view as a fundamental human right. London's top hotels still charge upwards of £10 a day for it, despite selling rooms for thousands per night. It all seems a little grubby when you can nip next door to Starbucks and use its WiFi for free. (But not the toilets. Never the toilets.)

Gia Cavalli, digital content editor at Forevermark (part of the De Beers Group of Companies) told me: "A luxury brand is defined by the elevated experience it offers. Failure to hold our digital presence to the same standard we apply to our products and in-store, risks compromising the very definition of ourselves as luxury."

Forevermark thinks of its website as a 'flagship store' – everything, from design and usability to content, must reflect its position as diamond experts. But it's not just about websites. As McKinsey says, "maximising digital impact is not as simple as building a better website or sending more messages into the Twittersphere".

Luxury brands must get to grips with their own customers' journeys to and around the brand. And give a consistent brand experience on- and offline. Nick Allen, client partner at The Brooklyn Brothers, explains how they apply this to Jaguar Land Rover. "Within luxury it's critical to carve out a distinctive positioning across digital channels that links to their character and archetype. For Jaguar, we brought to life the Art of Performance through digital and social experiences to launch the Jaguar F-TYPE and the Jaguar XE. For Land Rover, we were launching to an all-new urban audience. So we amplified the idea of going 'Above and Beyond' through multi-screen platforms."

Luxury brands typically understand their customers and expectations more than any other sector. But for some reason many still offer a generic or substandard digital experience. I recently bought a magazine and received a free sample from a not cheap make-up brand. Unsure how to use their new wonder product, and unwilling to waste it, I turned to YouTube to find out how to apply it. But the brand hadn't posted a single 'how to' video. Instead I found tonnes of amateur videos. Teen girls whacking it on with 200 other products before heading to tequila night at the student union. It was all very offputting. And off brand.

Your customers don't distinguish between online and offline anymore. If you want your brand to remain distinguished as luxury, then make sure your digital experience is luxurious too.