One of the most common ways of licensing publications on an Open Access basis is to use a Creative Commons licence (the link directs you to the Creative Commons UK website).
Creative Commons licences are ways of informing readers what they can and can't do with a published work, and offer a middle ground between the "all rights reserved" approach of copyright and the "anyone can do anything" approach of the public domain - in other words, the philosophy of Creative Commons can be summarised as "some rights reserved".
Creative Commons licences provide a range of limitations that can be placed on the use of a published work - you can discover the variety of limitations at the Creative Commons choose a licence web page. For example, you could allow people to freely distribute your work but not alter it in any way; allow people to alter your work, but derive no commercial advantage from it; and so on.
The RCUK Open Access Policy requires that any journal articles or published conference papers arising from RCUK-funded work made available on a Gold Open Access basis must carry a Creative Commons Attribution Licence, abbreviated as CC-BY. This is a very open licence that allows academic publications to be distributed freely, text mined, and incorporated into other works, provided that attribution is given to the authors.
Of particular interest to researchers in the Humanities and Social Sciences will be the OAPEN Guide to Creative Commons, which addresses many of the questions such scholars ask in relation to these licences.