This article analyses the factors underlying public attitudes in Britain towards recent attempts to provide the EU with a constitution. In the context of the incremental constitutionalization of the EU, this article represents a detailed assessment of attitudes in a traditionally Eurosceptic country. It builds upon insights from existing strands of work analysing public opinion on EU-related issues. The impact of economic interests, national identity, party cues and political sophistication are assessed using data from a single-country and a crossnational survey. The data are analysed using binary logistic regression estimation. The main findings are that both party ‘cues’ and national identity play an important role in underpinning public opinion. These findings hold up when general support for the EU is accounted for. There are mixed findings in relation to the sociodemographic factors. The findings provide important clues as to what structures public opposition towards further political integration.