We measure the size-mass relation and its evolution between redshifts 1<z3x10^9^ M_{sun} at 1<z5x10^9^M{sun} at 2.5<z<3, and at a fixed stellar mass, we find galaxy sizes evolve as R_eff{prop.to}(1+z)^-1.05+/-0.37^. The intrinsic scatter is <0.1dex at z<1.5 but increases to ~0.3dex at higher redshift. The results are in good agreement with those obtained in blank fields. We evaluate the uncertainties associated with the choice of lens model by comparing size measurements using five different and publicly available models, finding the choice of lens model leads to a 3.7 per cent uncertainty of the median value, and ~25 per cent scatter for individual galaxies. Our work demonstrates the use of strong lensing magnification to boost resolution does not introduce significant uncertainties in this kind of work, and paves the way for wholesale applications of the sophisticated lens reconstruction technique to higher redshifts and larger samples.

Cone search capability for table J/MNRAS/501/1028/table1 (Catalogue of lensed galaxies at redshift 1<z<3 which meet the selection criteria described in Section 2.3)