Tee Gee,
Unfortunately I have already dug them up and disposed of the roots. There was plenty of root on the plant, it took me ages to dig them up. I chopped the roots of the plants and binned them, composting the rest of the foliage.
I do believe it to be something to do with the roots though. This is my first year on the plot and I didnt realise you shouldnt hoe around sprouts. I hoed around at least 4 times, mainly to clear weeds.
Guess it is just one of those things I will remember for next year.
Thanks for the advice.