The overall goal of this project is to identify technical problems and potential barriers to the exploitation of Global Navigation Satellite Systems (GNSS) in the UK for safety-critical applications. This can be done best through a short, focused and dedicated effort to bring people together. Our aim is to bring together academic and industrial partners from the UK and overseas to focus on GNSS systems operating in different environments and the problems that they encounter.GNSS encompasses all Global Navigation Satellite Systems such as GPS (Global Positioning System) and Galileo. GPS has become a consumer technology and for many applications it is entirely adequate. However, there are a number of systems that require more than accuracy - integrity is vital. Integrity is a term used in the GPS community that refers to knowledge of the reliability of the navigation solution. Guaranteeing the integrity is a tricky problem. Problems that can occur that affect integrity include interactions of GPS signals with the local environment (e.g. buildings) and interactions of GPS signals with the Earth's atmosphere and ionosphere. This project will unite industry, academia and representatives from the GPS user community to identify GPS integrity threats and will form strategies to deal with them in the future.