Sometimes if you have an allotment association near you they will let you buy seeds at their club's purchase rate . ( bigger orders for such clubs get big discounts direct from the seedsman like Suttons , Fother gills etc etc ) .
Of late I've been and purchased a few packs of giant veg seeds off a guy on the internet called Clive Bevan. there are not many sees but if they do as he says they should then I'll be happy for some of the old bigger variety tasty veg instead of the commercial stuff the most seedsmen sell now adays .
I don't have Clives addy to hand but will hunt for it .... yer tis " giantvegetableseed.co.uk "
There is also another place on the net ... it is a penny club where members pay a penny or similar to belong to a club .
As a member your entitled to cheaply purchase their own produced seeds , all members are encouraged to grow some thing for the seed bank.
They don't need to have pased EEC seed tests .
If you do it , as a club , it helps keeps alive the older species /types that the commercials don't want because they do not sow , crop , harvest or store very well when using machines.
There is an amazing pea called telegraph which can hit 12 feet high or long if you grow it in a pig wire arch This seed source is called " realseeds.co.uk "
it is worth a look i have some of their capsicum seeds