It may be the slowest viral marketing campaign in the county's history, but in the age of emails, texts and tweets a mid-Norfolk food festival is using yeast, sugar and a bit of patience to help spread its message.

Organisers of the Brecks Food and Drink Festival have launched a friendship cake, the bakery world's equivalent of a chain letter, that is fanning out from home to home to raise awareness of next month's celebration of local produce.

Recipients are presented with a yeasty mix and a 10-day schedule of when to stir and add ingredients before dividing it into five batches, baking one and passing the rest to friends who start the process again.

Festival organisers have asked participants to also pass on information about the three-day celebration in and around Swaffham from September 14-16.

After experimenting, members of Beachamwell WI settled on a recipe using locally-milled flower from Heygates Farm and Norfolk carrots.

The two original batches prepared in June have now spawned an estimated 525 cakes, and CoCoes caf� at Strattons Hotel in Swaffham has incorporated fruits such as raspberries and blueberries.

Hotel director Vanessa Scott said: 'I know people groan about chain letters, but when you give someone a cake you can't actually ignore it. Even people who don't necessarily want to do it are on a guilt trip so they feel they have to do it. I think you can't help but get carried away with it. It brings you back to the basics and that's what it's all about.'

The novel marketing campaign has won the backing of South West Norfolk MP Elizabeth Truss, who will officially open the festival with Dr Pixie McKenna, who presents Embarrassing Bodies on Channel 4.

Ms Truss said: 'I love the idea of the friendship cake. It's a great way of promoting the Brecks Food Festival and getting more people cooking too. It also shows the friendliness and innovation of Swaffham.

'I am a keen baker and enjoy taking part in making the cakes. We have fantastic producers and chefs in the Brecks and the word needs to be spread. The Brecks Food Festival had a fantastic first year and I know this year will build on that. It's about the unique food we have in this area and encouraging people here and far and wide to take part in it. With the recent visit by the chief executive of Visit England and the lottery grant, the Brecks has real momentum.'