There are three main codes of practice that a journalist should pay attention to:
Ofcom:
Simply put, Ofcome regulates all types of broadcasters. They have the power to fine companies, ban programmes and even shut down broadcasters by revoking their licences. Ofcom demands impartiality from its broadcasters and also makes sure no broadcaster shows bias.
PCC:
PCC stands for Press Complain Commission. The PCC regulates magazines and newspapers and is quite a mild form of regulator. Their code doesn't mention impartiality thus newspapers can get away with bias.
BBC code:
The BBC code is a self made guide for employees of the BBC and is similar to that of the PCC however they insist on absence of bias.