The dataset details greenhouse gas fluxes as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) across six intertidal sites in the winter and summer of 2013. Three of the sites were in Morecambe Bay, North West England and three of the sites were in Essex, South East England, each of these sites consisted of a saltmarsh area and adjacent mudflat area, twenty two sampling quadrats were placed on each area. Light and dark incubations were performed using a benthic chamber on seven of the twenty two quadrats of each site. This data was collected as part of Coastal Biodiversity and Ecosystem Service Sustainability (CBESS): NE/J015644/1. The project was funded with support from the Biodiversity and Ecosystem Service Sustainability (BESS) programme. BESS is a six-year programme (2011-2017) funded by the UK Natural Environment Research Council (NERC) and the Biotechnology and Biological Sciences Research Council (BBSRC) as part of the UK's Living with Environmental Change (LWEC) programme. Full details about this dataset can be found at https://doi.org/10.5285/186fdb05-cc14-4315-be30-fec28048b310