Overt Recording
If all parties know that a conversation or actions will be recorded, the recording is overt. Anyone opposed to the recording can decline to give their permission and the recording should therefore cease.
Covert Recording
Covert recordings are those that are made without the knowledge of the subject of the recordings.
Covert recordings can be made by bodies who are authorised to do so but they are subject to compliance with the Regulation of Investigatory Powers Act 2000 (RIPA).
Covert recordings that do not comply with RIPA either because they are carried out by an unauthorised body or because the RIPA regulations are breached, maybe unlawful and may breach an individual's human rights.