The good and bad of Cadbury's brand association tendencies by Helen Edwards, PPA, Business columnist of the year, 21.03.2012

Brand equity can thrive or wither depending on the choice of partner for a tie-up, as Cadbury's disparate relationships demonstrate. There are two places where you might encounter the Cadbury chocolate brand, aside from the normal confectionery shelves and biscuit aisles.

The first will be familiar to rail users. You're languishing in the queue in a travel branch of WH Smith. When you finally reach the till a bored assistant asks whether you wish to avail yourself of an industrial-sized slab of Cadbury Dairy Milk at half price. The other potential encounter is altogether more refined. It awaits you in the chiller cabinet of your local supermarket, where you will find the newPhiladelphia spread blended with Cadbury's milk chocolate - if they haven't sold out already. Either way, as a marketer, you're looking at examples of brand-to-brand relationships - the ones brands have with each other, leaving consumers either playing gooseberry, or enjoying the fruits of the union.

Make-or-break relationships These relationships come in varying formats and intensities (see 30 seconds), but, as the Cadbury examples illustrate, a single principle governs them all: they can potentially build brand equity, or destroy it. It's easy to see what WH Smith might get out of its partnership with Cadbury. This muddle of a retail brand finds a way to keep some customers coming back and enjoys a mild glow from its association with one of Britain's best-loved brands.

What Cadbury gets out of it is harder to fathom. At first, it felt like a short-term promotional tactic, but even at that level appeared equity-threatening. The longer it persisted, the stronger became the association between those sensual mauve swirls and the WH Smith checkout experience - something no self-respecting brand should want to be integral to.

Cadbury and Philadelphia, conversely, is a marriage made between two versions of heaven. Facilitated through their joint ownership by Kraft, it creates something new and pleasurable for the consumer, brings two strong brands together with deft complementarity, and inspires a positive social-media buzz.

The Triangle Test Whether brand-to-brand relationships are light-touch and temporary or solid and longer-term, they need to pass, as Cadbury-Philadelphia does, the Triangle Test. Simple in theory but subtle in practice, this demands that the relationship offer clear benefits to both participating brands, and the consumer. It's a three-way love-fest: if only two parties are satisfied, the test is failed and the relationship flawed. The triangle test would call into question some current, high-profile relationships. The Marni diffusion range at H&M, for example, is certainly a big hit with consumers, and is clearly a boost for the retailer. It is less clear what Marni gets out of it - an entree to a younger target, perhaps, but one that is not guaranteed ever to trade up from an £80 garment to an £800 one.

Meanwhile, airline codesharing is an example of brands falling for each other and forgetting about the hapless, confused consumer. You book with British Airways, but the small print says your flight could be operated by another carrier. This could be an airline called S7 - otherwise known as Siberia Airlines. Happy with that?

Brand-to-brand relationships are like all relationships: difficult, complex, but potentially tremendously enriching. Conveniently, Cadbury shows you how to go about it - and how not to.

30 SECONDS ON: BRAND RELATIONS No brand is an island. Here are some of the ways in which brands link up with one another. - Charity specials: (RED), the brand name for the Global Fund charity (raising money to eliminate AIDS), is notable for selling its products only in conjunction with other brands. There's a (RED) AmEx card, Dell laptop, Converse shoes ... but (RED) doesn't have any offering of its own.

- Trial-size placements: It's no accident that you find Molton Brown products in Marriott hotel bathrooms. The former gets exposure to an upscale customer base, the latter enjoys a good deal on luxury skincare products.

- Designer diffusion ranges: Stella at Adidas, and John Rocha, Jasper Conran and Matthew Williamson at Debenhams are all part of this burgeoning trend.

- Co-branding: In 2006 Apple and Nike joined forces to create 'Nike+iPod', a kit comprising a chip (that slotted into compatible Nike trainers) and a transmitter (that fitted into your iPod). The chip can transmit stats such as distance run and calories burned to the iPod.

- Strategic alliance: The airline sector is big on this one. Fly round the world with Star Alliance and you could get to sample the delights of up to 26 different airlines.