The English House Condition Survey (EHCS) is a nationally representative continuous survey which is run by the Office for National Statistics (UK) on behalf of the Office for the Deputy Prime Minister (ODPM). The EHCS is a multi-stage survey and the survey unit is the dwelling. Following a face-to-face interview with the current occupants and a physical inspection of the property there is a follow-up desk based survey. This is called the Market Value Survey (MVS) and includes the collection of the dwelling's market value and other supplementary questions relating to housing demand and the local area. The MVS is conducted via a web-based questionnaire completed by professionally trained property valuers. Pivotal to a successful MVS is the extrapolation and display of background data (from the earlier interviewer and building surveyor administered parts of the survey) such as property descriptions and digital photographs. This paper explores how quality was ensured when moving these data between the different parts of the survey. There will also be a focus on the practical considerations of official web data collection such as item non-response, on-line data validation and data confidentiality.