Top garden designer and twice Chelsea medal-winner Hannah Gender took a break from exhibiting at the famous flower show this year as she prepares her plans for an organic vegetable show garden at next year's event.

She has been gaining inspiration from allotment holders nationwide while filming Digging For Victory, a UKTV series she is presenting with Blue Peter gardener Chris Collins, to find Britain's best allotment.

On her travels, Hannah has met many allotment holders who are growing local heritage varieties of vegetables.

She says: "Old heritage plants have been lost over the years because they didn't crop at the same time, which is what commercial growers want, but on an allotment you don't want everything cropping at the same time so they are ideal.

"Also, the taste of the produce is better and the old-fashioned plant will build up disease resistance. It tends to survive. Hybrid strains eventually get weaker."

Indeed, thousands of vegetable varieties have been lost in this country since the 1970s. For example, the Victorians grew more than 120 different varieties of tall garden pea, providing a continuous picking of freshly shelled peas throughout the summer months.

A century later, frozen food manufacturers require varieties where all the peas ripen at once which makes for quicker harvesting. Consequently, tall pea varieties have fallen into disuse.

Every year, before a variety can be sold, it has to be registered on the national list of recommended varieties, which is a way of controlling the quality and authenticity of seed sold, but is also expensive enough to discourage the sale of seed of vegetables that do not have a mass market.

This means that old varieties which suit the home gardener but not the commercial producer are deleted from the list and are no longer available.

Why are old heritage seeds so important? With the prospect of global warming, we may have to contend with new types of pests and diseases. Varieties that have been bred for today's conditions may prove unsuitable under changed conditions. So, we need to keep as broad a genetic base as possible.

Some of our older varieties may contain valuable genes that could be vital to plant breeders in future breeding programmes.

There's also the seed-saving issue. Seeds taken from a hybrid may either be sterile or more commonly fail to breed true, while open pollinated seeds, the traditional varieties, adapt to the local ecosystem, as opposed to modern hybrids, which are static.

Organisations such as Garden Organic (formerly the Henry Doubleday Research Association), the national charity for organic growing, as well as those who hold National Plant Collections, are trying to preserve our heritage.

Garden Organic has a collection of 800 old and unusual vegetable varieties, collected over the years, including several late 19th century tall peas, including Champion of England and Ne Plus Ultra.

Hannah Genders recommends that gardeners who want to try out old heritage plants should contact Garden Organic, which has its own heritage seed library.

The library aims to conserve and make available vegetable varieties that are not widely available. Members receive a choice of up to six varieties and there is also also an informal seed swap section run between members. For details go to www.gardenorganic.org.uk * Digging For Victory is on UKTV Gardens at 10pm on Fridays.