Sir, As highlighted in your feature ('Brand Stretch...or Brand Snap?', 9 October), taking your brand outside its core proposition remains a risky business.

We always ask three simple questions when approaching a brand extension brief. Does the extension express the parent brand vision? With Marmite, the extensions into cereal bars and chocolate reinforce the position that Marmite is a quirky, individual brand.

Does it have a product truth? There needs to be a link between the parent brand and extended product. For example, with Warburtons' Chippidy Doo Daa there was credibility in the bakery heritage that made it a good fit for a baked snack product.

Does it bring something new to the category? Where there are already strong players in the category, brands need to provide something different to excite the consumer and promote change.

If you can't demonstrate a clear rationale on all of the above points then a brand extension rests on shaky ground.

Ben Harris, brand development director, Anthem (branding and design agency)