Pink poppy. Self seeds everywhere.....

an annual opium poppy, Papaver somnifera. Come in a range of colours, white, red and many shades of pink in between. They can also be singles of fully doubles.
they are prolific seeders so if you don't want lots more remove them immediately after flowering.
If you didnt grow them last year then this is seed left in the soil from previous years. They are viable for years and every time you dig the soil and expose the seed to the light they will germinate.

Many thanks for the replies. They'll be staying for now and hopefully get some cracking flowers