If you can't find the seeds in the UK, here is a link to a dutch company. They only sell native seeds.
The price is € 1.45 a packet + shipping. Don't know if they ship to the UK, and how high shipping costs are, but if you want I could order them for you if you're are willing to pay the extra shippingcosts from here to you (€ 0,90).
I have a lot of family in the Netherlands, so if they don't ship to the UK, I will order them via them.