To be eligible for submission in the next REF, research outputs must be deposited correctly within PURE within a specified (and short) time period.
This is typically within three months of "acceptance", subject to publisher restrictions and embargos.
More information about this is given in the link to "The next REF" below. From that link, click through to the "HEFCE (Higher Education Funding Council, England) Circular letter 07/2014"
The next REF
The letter on that page is equally relevant for the Scottish Higher Education Funding Council.
Put it into PURE
Deposit information about your Research into the University Research Information system PURE, to make it open.
Deposit your publication