Rory, the leaves look like something in the daisy family, but the whorled pattern of the emerging leaves isn't familiar to me. If you can post an update in a couple weeks it will help.

It looks somewhat like Saponaria officinalis to me. You can see some inages for comparison here: https://www.illinoiswildflowers.info/weeds/plants/soapwort.htm

It would be nice if it's Saponaria officinalis. We shall see.

It isn't S officinalis. That, being a member of the Caryophyllaceae, has opposite leaves. They are also blunter in shape, smooth almost succulent in texture and have pronounced parallel leaf veins.

It's probably an undesirable weed. Those are the only things the deer and rabbits don't eat.