Lotus corniculatus (bird's-foot trefoil) and L. pedunculatus (greater bird's-foot trefoil) have the potential to contribute nutritional benefits to grass–legume swards in temperate regions, but there is a lack of information on their competitive ability in such mixtures. This experiment compared the sward contribution and condensed tannin (CT) content of nine Lotus varieties established in plots on a low-fertility upland site in Wales, UK, containing mixtures of meadow fescue (Festuca pratensis) and white clover (Trifolium repens) varieties of different leaf size, or without white clover (control). Total dry-matter (DM) yields and Lotus DM were evaluated in two cuts in each of three harvest years, with CT content of Lotus measured at Cut 1 in each year. Lotus corniculatus varieties were significantly higher yielding than those of L. pedunculatus, except in Year 3. In all cuts, except Cut 1 in Year 1 and Year 3, the presence of white clover increased total DM yield compared with the zero-clover treatment. Total DM yields were higher with large-leaved cv. Katrina than with small-leaved cv. AberAce except for Cut 1 in Year 1. Annual Lotus DM yields were significantly higher in the presence of white clover, except in Year 3, but were not significantly affected by white clover leaf size. The highest concentration of sward CT (17 mg g−1 of sward DM) was insufficient to bring about measurable environmental benefits. A Lotus breeding programme aimed at increasing the leaf/stem ratio within persistent germplasm could be pursued to ensure delivery of appropriate levels of sward CT.