University ethics committee vary in their practice but each is likely to have a code of practice which will indicate what ethical standards are required. An example of a flowchart which shows the stages to obtaining ethical review at a higher education institution is here. At a basic level, projects are likely to be expected to produce their research plan including a rationale, together with examples of consent forms or recording agreements, as well as information sheets. They are also likely to indicate awareness of such issues as risk assessment, deposit agreements and an indication that in carrying out the work the contribution of others and use of relevant source materials is acknowledged. An example of a REC application form (from Royal Holloway, University of London) is here.
The UK Data Archive has produced helpful guidance for researchers when approaching and working with RECS here.