In theory you can now only sell seeds commercially if they are varieties which have been tested for the safeness of the food they produce. Only the high volume commercial varieties are tested. There is concern that this is going to result in a rapid loss of about 99% of our genetic diversity in food plants. Special repositories of vegetable seeds are being set up to preserve that diversity.

Some sellers get around this to sell you garden varieties by getting you to join a club for a nominal fee. One who does that is www.realseeds.co.uk They specialise in varieties which are tested as good for the garden.

Another method is probably to sell the plants as ornamentals. After all, Dahlias were originally bred as food plants.

Yet another method is to buy the seeds from abroad. I don't know how legal it is, but there doesn't seem to be any difficulty in achieving it in practice.

So the big boys who have to be seen to be following the rules. Don't by your vegetable seeds from the big boys, buy them mail order from little sellers who specialise in garden varieties.