[Bumblebear]

It is tall and I haven't seen it in any books or on websites.  The closest thing I have found was nipplewort, but the leaves aren't round....

[deepinthewoods]

it looks like a variety of dandelion?

[Fleecewife]

Do you have a pic of an open flower?   It could be a hawkweed or a lettuce.  Flower pods are like groundsel but leaves are not.   Does it have milky stuff in the stems when you cut them?
You can see why it's common in your garden with all those seeds blowing around 

[SallyintNorth]

Sow thistle?

[Fleecewife]

Sow thistle?

That's it Sally 

[colliewoman]

Yup definitely sow thistle!
My rabbits have eaten the lot here

[feldar]

We call it milk thistle here, the sap is milky white when the stem is broken, it is good stuff for pet rabbits and guinea- pigs.

[Bumblebear]

Thanks everyone    Shame I don't have rabbits then.......

[hexhammeasure]

yup milky thistle... we feed it to the hens..then the leftovers go to the compost

[Sylvia]

Sows love it too, it increases milk yield!

[Mammyshaz]

yup milky thistle... we feed it to the hens..then the leftovers go to the compost

This is good to know  sometimes a sneaky one pops up between the veg. Will try the hens with it. I like free treats