In October 1998, EU legislation made the fitting of electronic immobilisers mandatory on all new cars in the UK. This has been widely recognised as an effective method for reducing the risk of vehicle theft. However, to date there has been no systematic evaluation of the effectiveness of introducing electronic immobilisers in this way. This paper reports on a study that set out to measure the ... [Show full abstract] effectiveness of the EU legislation on car theft patterns in the UK. Using data from the Home Office Car Theft Index, two competing theories that predict how improved vehicle security would affect vehicle theft rates over time were examined. The study finds evidence that compulsory immobilisation of vehicles has been effective in reducing theft rates. However, there would also appear to have been some displacement towards both older and newer vehicles, although this is outweighed by overall gains in terms of lower theft rates. The study concludes with a recognition that further research is required, based on disaggregate data, rather than on the aggregate statistics presented in this paper.