It will vary from place to place. Where I previously worked in HE, representatives of the academic and administrative staff of the Faculty would hold a Board of Examiners meeting, where they sat down, looked at everyone's marks and confirmed they were correct, and then took decisions on what to do about any oddities (for example, where people had failed a module, or had mitigating circumstances). We did look at borderline grades, but only where people's final degree grade was affected (i.e. if someone had achieved 59.5% overall, the Board would probably decide to award them a 2:1 rather than a 2:2) but we wouldn't have done it for first year marks.