The influence of trophic status on CH₄ production, emission and stable carbon isotope composition was investigated in two ombrogenous and two minerotrophic peatlands situated in Wales, UK. Methane production and emission rates were highest in the minerotrophic peatlands and CH₄ in both pore water and emissions to the atmosphere were notably ¹³C-enriched compared to the ombrogenous bogs. Highly negative δ ¹³C values (−95 to −82‰) for CH₄ flux from the acidic rainfed peatlands likely resulted from a combination of CO₂/H₂ methanogenesis and isotope effects associated with diffusion of CH₄ through aerenchymatous tissue of vascular flora. The δ ¹³C values presently attributed to CH₄ flux from northern wetlands in isotope-weighted mass balance budgets of the CH₄ cycle may be too positive. Methane flux from northern bogs and fens should be assigned different δ ¹³C values because CH₄ is notably more ¹³C-depleted in the former, albeit emission strength typically is weaker.