Oxbridge vacancies
A word of caution: many of the college vacancies are non-stipendiary fellowships, i.e. they do not pay a salary only a small amount of expenses and free meals, or other perks. It is expected that you will be employed by the department or have some other source of postdoctoral funding. For that reason, you should always check the Mathematics Institute page first. Nonetheless, actual paid fellowships do appear, so it's worth checking the individual college sites periodically.
Oxford college vacancies: open them all at once or: All Soul's, Balliol, Brasenose, Christ Church MISSING, Corpus Christi, Exeter, Harris Manchester, Hertford, Jesus, Keble, Kellogg, LMH, Linacre, Lincoln MISSING, Magdalen, Mansfield, Merton, New, Oriel, Pembroke MISSING, Queen's, St. Anne's, St. Catherine's, St. Edmund Hall, St. Hilda's, St. Hugh's, St. John's, St. Peter's, Somerville, Trinity, University, Wadham, Wolfson, and Worcester.
Cambridge college vacancies: open them all at once or: Christ's, Churchill, Clare, Clare Hall, Corpus Christi, Darwin.