RCUK recognises a journal as being compliant with this policy through the Green route if:
The journal consents to deposit of the final Accepted Manuscript in any repository, without restriction on non‐commercial re‐use and within a defined period. No APC will be payable to the publisher.
In this latter case, in STEM disciplines, RCUK will accept a delay of no more than 6-12 months between on‐line publication and the final Accepted Manuscript becoming Open Access. In the case of papers in the arts, humanities and social sciences (which will mainly be funded by the AHRC and the ESRC), the maximum embargo period will be 12-24 months.
In most cases this can be achieved by depositing your paper into BURA, but MRC, BBSRC and ESRC have specific subject repository requirements. Please check the details here.
You can use the SHERPA/FACT database to check whether your journal offers a compliant publication route, and which route to opt for.