Background: The peer review of clinical research projects is an essential step in project preparation. While some projects undergo rigorous review by grant-giving organizations, this does not apply to all clinical research. In many cases, peer review, if undertaken at all, is not rigorous, fully independent, or timely. Depending on their department or institution, many researchers do not have easy access to such review. This can result in delay to ethical and institutional approval, and uncertainty about the quality of individual projects. Methods: After a two-year pilot study the Peer Review Service (PRS) was established at Imperial College, London in 2009. The aim was to provide an easily accessible and quick service for researchers at all the clinical sites associated with Imperial College. A graded system of review levels was designed which used an algorithm to match the independence and robustness of the review to the ethical weight of each project. The levels ranged from 1--internal review by a supervisor to 5--fully independent review by at least two external individuals. A semi-structured response form for reviewers was generated to facilitate the review process and ensure that all relevant aspects were considered. For each reviewed project, the PRS issued a certificate confirming the quality of the review. Outcomes: There was a gradual increase in use of the service from the 2009 inception. From January to June 2020, 63 projects underwent peer review commissioned by the service. This represented all of the clinical research projects performed at Imperial sites that required review. The mean time from application to delivery of review was 1.73 weeks. Administrators found the algorithm for determining the peer review level easy to use, occasional queries being managed by members of the supervising committee. Audits demonstrated that researchers, reviewers and ethics committees were satisfied with the service. Conclusion: A proportionate system of peer review for clinical research projects works well. It produces appropriately robust and independent reviews and can be implemented easily by administrative staff. Close association of a peer review service with university research administration ensures that all projects needing peer review receive it. The centralized service assists researchers in obtaining reviews speedily. This simple model could be used widely by other clinical research centres.