The study investigated the effects of lamb genotype produced from hill flocks on feed efficiency, carcass characteristics and meat quality in animals finished on either a high forage:concentrate ratio diet (HFC) or a low forage:concentrate ratio diet (LFC). Purebred Scottish Blackface (BXB) lambs were compared with Blue-Faced Leicester×Scottish Blackface (BLXB) and Texel×Scottish Blackface (TXB) lambs. Purebred Cheviot (CXC), Suffolk×Cheviot (SXC) and Texel×Cheviot (TXC) lambs were also investigated. Lambs on the LFC diet were offered grass silage and concentrates mixed in the proportion of 0·80 silage and 0·20 concentrates on a dry matter basis. The LFC diet consisted of 0·20 grass silage and 0·80 concentrates on a dry matter basis. Representative lambs were slaughtered at the start of the experiment and on reaching 38 and 46 kg live weight. Averaged over the two slaughter weights, within the Blackface cross lambs, BXB had a lower liveweight gain (P < 0·01) than either BLXB or TXB (138, 207 and 203 (S.E. 11·1) g/day, respectively). Within the Cheviot cross lambs, CXC had a lower liveweight gain (P < 0·05) than SXC (188 v. 220 (S.E. 11·1) g/day), while SXC and TXC (204 g/day) had similar liveweight gains. Lambs on the LFC diet had a higher dressing proportion (P < 0·001) compared with lambs finished on the HFC diet (0·466 v. 0·434 (S.E. 0·0018) kg carcass per kg live weight). Averaged over the two slaughter weights BXB lambs had a lower (P < 0·05) dressing proportion than the other genotypes. Carcass conformation classification (assessed on a five-point scale) was higher (P < 0·001) in lambs finished on the LFC diet (3·0 v. 2·4 (S.E. 0·04)). Conformation classification was higher in lambs produced from Cheviot compared with Blackface ewes (P < 0·05). Within the Blackface cross lambs, BXB and BLXB lambs had a lower conformation classification (P < 0·001) than TXB lambs (2·4, 2·4 and 2·9 (S.E. 0·08) respectively). Within the Cheviot ewes, TXC lambs had a higher (P < 0·001) classification than either CXC or SXC (3·1, 2·7 and 2·7 (S.E. 0·08) respectively). Lambs finished on the LFC diet had a higher fat classification score compared with lambs on the HFC diet (P < 0·001) (3·4 v. 2·8 (S.E. 0·04)). Fat classification was similar across all genotypes. Lambs finished on the LFC diet had a lower ash content in the carcass than lambs finished on a HFC diet (P < 0·01) (44 v. 47 (S.E. 0·8) g/kg). Lamb genotype and dietary forage:concentrate ratio had no significant effect on cooking loss, sarcomere length, Warner–Bratzler shear force and L* values. Ultimate pH (pHU) was not influenced by dietary forage:concentrate ratio, but was significantly (P < 0·01) higher in BXB lambs compared with BLXB, TXB, CXC and TXC lambs. Lambs offered the LFC diet during the finishing period had significantly higher values for a* (P < 0·05), b* (P < 0·001), C* (P < 0·001) and H0 (P < 0·05) than lambs offered a HFC diet. Of these parameters only b* was significantly affected by lamb genotype, with BXB lambs having a lower value (P < 0·05) than the other genotypes.