How pretty. My first thought was night scented stocks but I think they only have four petals. If nobody else comes up with a name, call your local council grounds men, they can tell you.

Looks like Cuckoo Flower, also called Lady's Smocks to me. It's a very pretty wild flower but does spread as is evident from the picture.

It's not Lady's Smocks, those only have four petals - its definitely one of the Phloxes, but its hard to discern just how tall the plants are - might be Phlox glaberrima or a variety of, depends on the height.

Stunning! I agree it's Polemoniaceae, which includes stocks, but no idea which one.

it reminds me of Viscaria.

Could be Viscaria oculata - but would they really plant annuals on a roundabout? Most councils are, or have, switched to more permanent planting to save money, well, in West London anyway.

people sometimes green bomb them, but East Yorks uses annuals regularly. we have several special needs educational nurseries and the students are trained in horticulture. their teams plant out the local roundabouts.

Our council has sown poppies and cornflowers this year and last. They look nice now but a mess later in the summer. These are lovely aren't they?

viscaria oculata wins the day