An office affair might add some spice to the daily grind of work, but it can have consequences for your career. Whilst UK companies tend to steer clear of the "love contracts" used by some US employers to ban workplace liaisons, you should consider the impact of beginning a relationship with a colleague and manage the situation carefully.
Some companies may tackle office affairs in their code of conduct and all will expect staff to maintain certain standards of behaviour. You cannot be fired for an office romance however, and the right to a private life is protected by the Human Rights Act 1998.
Your employer might have policies around relationships with colleagues that you should adhere to. You may not be able to supervise or be managed by a partner and companies might also insist that you work in separate departments. Relationships break down at it can be awkward for everyone in the workplace if feuding ex-partners are located together.
An office affair might impact on your career prospects regardless of what the law states. Other colleagues or managers might be jealous or simply disapproving of the relationship. People working around you might feel uncomfortable, particularly if there is an ugly break-up to the relationship. You should avoid any type of intimacy or physical contact in the workplace, and maintain a professional stance in all dealings with your partner.
Tell your boss
There is no obligation for you to tell an employer if you embark on a workplace relationship but being honest about it is probably the best course of action. Word is likely to get out somehow and you run the risk of being seen as dishonest if you keep it secret. If you manage or are managed by the person you are seeing it is even more important to be upfront and let management know.