Following the invention and proliferation of the Internet, Web and mobile technologies, we have seen a global revolution in retailing. Despite the rapid growth of e-commerce, the online grocery shopping market has taken until now to gain traction, currently constituting 6.9% of the UK's grocery market, but projected to increase 68.3% to 17.6 pound bn by 2021. There is little work accounting for new and contingent behaviours in the online grocery market, not least because of historically poor access to retailers' data. This paper leverages access to the UK's fourth largest supermarket, WM Morrisons Plc (Morrisons) to investigate consumer behaviour in this market, augmenting the Office for National Statistics' Living Costs and Food Survey, the UK's only substantial publicly available resource to date. This paper establishes that there have been changes in consumer behaviours in response to the unique opportunities and challenges of online grocery shopping and explores the specific socio-technical factors that may be contributing to these changes, namely: ease of price comparison; attitudes to purchasing perishable goods online; and logistical considerations. Furthermore, it provides some evidence that the proportion of fresh products bought online exceeds the proportion bought offline, contrary to popular belief. Finally, this paper argues that with correction for location bias, the Morrisons sample could provide a proxy for examining online grocery behaviour in-depth at the national level.