Partial root-zone drying (PRD) is a deficit irrigation technology that exploits early root sensing of soil drying prior to any hydraulic stress and the chemical signals (e.g. ABA) that are generated, to modify shoot physiology and growth. In Australia PRD has been implemented in vineyards with significant improvements in irrigation water-use efficiency, decreased vegetative vigour and enhanced grape (and resultant wine) flavour and quality. Not dissimilarly, a top priority for the UK tomato industry is the improvement of quality and flavour to enhance tomato as a functional food crop. A PRD trial was established in a commercial glasshouse adopting the standard industry practice of soil-less culture with drip fertigation. Treatments comprised (1) plants rooted in single Rockwool slabs representing a current practice control (SSC), (2) plants with roots split evenly between two slabs with equal fertigation to both (DSC), and (3) as (2) but with fertigation alternated between each slab so that root halves experienced cycles of wetting and drying (PRD). Typically the PRD treatment significantly decreased leaf conductance (up to 30%), total sap flow (22% at mid-day) and decreased leaf area (24%), fresh weight (18%) and dry weight (22%). Individual fruit fresh weight and mean weekly yield through the season were not significantly affected by PRD, but PRD significantly increased both dry matter allocation (20%) to the fruit and the degree Brix (16%) compared to SSC treatment, with DSC treatment intermediate in response. Most significantly, the putative anti-cancer carotenoid lycopene was increased by up to 27% in PRD fruit.