Different kinds of research need different levels of peer review. In general, the greater the burden or potential risk to which the participants are exposed, the more robust and independent the review should be.
In order to help researchers identify the level of review needed for individual projects, the Peer Review service has developed a framework. This should act as guidance for you as to the level that will be required for your project.
The minimum requirements for peer review at each level are as follows:
Level 1 No peer review required
Level 2 Review by project supervisor or departmental colleague
Level 3 Independent internal review
Level 4 External review
Level 5 (NIHR) External review - Two reviews both of which are by experts external to the host institute
A set of examples can be found in the RGIT_SOP_040_Peer Review.pdf
Projects at Levels 3 and 4 should be processed through the PRO, the office can also provide the necessary support for levels 1 and 2 if needed.