The roots had actually split the side of the bucket and it was only held together by the thicker rim at the top. One slit with a knife and it popped apart.
This is what came out, the ruler is twelve inches long! Oh, and the variety is 'Dagger F1'
After trimming off all the thin ends and excess root I was left with 2.96kg or (6.5lbs) of parsnips from the one bucket. That, to me, is an exceptional yield and one which has prompted me to start a little competition for next year. No prizes but I'd like to see just how big a yield of any fruit or veg can be achieved from one 10 litre plastic flower bucket.