[RichardY]

Does anyone know if there is a major difference in the amount of root produced by the 2 different varieties. I'm guessing the Greater (Arctium Lappa) has the bigger root. More importantly is there a place in the UK where I could get some of the seed, despite being known as a weed I haven't seen any where I live. I did buy some Greater Burdock off Ebay, but the seeds failed to germinate  .

[DanielCoffey]

You could try Margaret Lear (PlantsWithPurpose) at https://plantsandapples.co.uk/ based in Perthshire as she grows herbs and plants and her husband deals with fruit trees.

There are no Burdock entries in her 2016 catalogue but she may be able to put you in touch with someone reliable.