Removing Comfrey

I'm trying to remove a patch of common comfrey because I'm a cretin and planted it in the middle of the veg garden where it self seeds everywhere! 
So far I've probably snapped 95% of the tap roots at the depth of a fork because my subsoil is boulders in clay, perfect for burying and hanging on to long roots  What chance it won't all just grow back?
On the plus side the soil is lovely underneath

I was invested with the stuff and after 7 years it is managable, on the deepest and thickest roots I had no choice but to poison them

Move house.

I can't!! We built this one and it isn't quite finished   

I'll just have to harvest a lot more often, I guess.

I have a lot of the white comfrey seeding everywhere - and have the same problems digging it up. Since I can't dig it out I've learned to accept it and regard it as beneficial!
If you keep cutting the leaves (before it flowers) and using them as mulch its all good. Being in the middle of your veg plot means you can just scatter them around your veg without having to walk anywhere.

PP, did your comfrey all come back? I'm wondering if I can reduce the size of the patch on the allotment and if there's any chance of growing something in that space.

Yes it did.
After digging out as much as I could, the patch spent a year under cardboard, the voles munched plenty and yet there's still seems to be almost as much. The drought last summer did slow it down a bit!

I have a lot of the white comfrey seeding everywhere - and have the same problems digging it up. Since I can't dig it out I've learned to accept it and regard it as beneficial!
If you keep cutting the leaves (before it flowers) and using them as mulch its all good. Being in the middle of your veg plot means you can just scatter them around your veg without having to walk anywhere.

I'm still trying to dig out the comfrey that's in the wrong place but I leave it growing around the fruit bushes and trees. Cutting off the leaves and dropping them around the bushes feeds them.
Maybe plant in the comfrey patch instead of trying to dig it up?

Thanks, PP. I had a feeling that might be the answer!

Veggie, what kind of things would be able to grow with pushy comfrey popping up around it and presumably the world's deepest most established roots hogging the ground?

I assume mine is a sterile variety - hasn't seeded around the plot although I let it get flowers for the bees, and has pinky/purple flowers. I think it's been there quite a while.