It is not clear from the photos, but I think the stalk of the middle leaflet it longer than those of the side leaflets, making this Medicago rather than Trifolium. Also the stipules at the bases of the main leaf stalks are torn looking, which fits Medicago polymorpha better.
I would say Medicago polymorpha from the toothed edges of the leaves and theappearance of the stipules. Medics have three leaflets with the central leaflet on a longer stalklet, but so does Trifolium dubium.
Thanks for pointing out about the central stalklet in Trifolium dubium, which is unusual for Trifolium. Vicflora separates Trifolium from Medicago on that character, and then states in the species description that the central stalklet is longer!