Possibly Corncockle or Agrostemma

Yes, I'd say corncockle, I had them in my free wildflower seeds last year and they have self sown this year. Be careful, they are toxic so wear gloves when you touch them.

Thankyou.

Hi, I had this in a mixed seed container, about 10 years ago, I still find and dig out a few every year, a very persistent annual, Derek.

Thanks Derek,I did the same thing so I now know what to expect.

They should grow taller than that in the ground. Toxic? don't worry -so are many other popular garden plants. They are only poisonous if you eat them anyway - handling them is no more dangerous than handling foxgloves.