Research Council Fellowships
These are given to post doctoral researches after the first few years of their career by institutions like BBSRC, MRC or the Welcome Trust. The general idea is that the funding supports notable scientists to help them establish research based careers. There is a limit to how long after obtaining a PhD you can apply for these, which is normally about 5 years but can be longer in some cases. These research fellowships require that a position in an academic department has been negotiated in advance, i.e. so there is office and lab space. A research fellow will typically become a member of the faculty in their academic department and will be a principle investigator. The department may require that the fellow take on certain teaching or other duties, but the position is not a formal lectureship position.
Collegiate Junior Research Fellowships
Junior research fellowships (JRF) are appointments made by colleges to researches at the very start of their career. In many instances the applicants will not have completed a PhD but will be in the final year of their PhD studies. Applicants do not have to already be members of the college that offers the fellowships, but a significant proportion of JRFs end up going to those continuing in the same college after a PhD. A JRF itself will often, but not always, come with a stipend (money) and will grant the holder various privileges within the college, which may include dining rights and accommodation. The position has no formal relationship to academic appointments within the university, but is generally designed to allow an individual to concentrate on research. Some JRFs are targeted to specific research areas, but many are not and thus scientists may be in direct competition with other academic disciplines.
These positions are offered by the various Cambridge colleges who wish researchers to do undergraduate teaching for the college. A college lectureship is not the same thing as a university lectureship; the researcher is not deemed to be a principle investigator. College lecturers become fellows (the academic administrators) of the college and gain the privileges that such a position bestows. Typically this will include dining rights, office use and in some instances accommodation within the college.