It depends on the Business School you are joining. If you are joining LBS, there will be a lot of recruiting activities ranging from company presentations and invite-only dinners to on-campus recruitment. LBS ist definitely the top MBB-feeder BSchool in the UK.
If you will go to Judge/Said, there will most likely be on-campus recruitment but there will not be as many recruiting events as at LBS. Other schools (e.g. Cass, Imperial) might not have on-campus recruiting activities at all and you will need to significantly rely on networking.