Working closely alongside each other day in, day out, means people often develop strong feelings for co-workers, but this can cause problems when the feelings aren’t mutual. If your office admirer won’t take no for an answer, it can make things very difficult for you, affecting your well-being as well as your work.
If you feel you are being sexually harassed at work, you should raise it with your line manager and your union rep, if you have one. Ask your manager to follow the company policy for tackling harassment. If the problem cannot be resolved, you will need to consider putting in a formal grievance and, if necessary, take Employment Tribunal proceedings. (A tribunal claim would need to be lodged within 3 months of the act concerned, even if the grievance is still being heard).
Harassment is where someone’s dignity is violated, or they suffer an intimidating, hostile, degrading, humiliating or offensive environment. Harassment on the basis of a protected characteristic is prohibited by the Equality Act 2010 - and if the harassment is of a sexual nature, it will amount to sexual harassment.
Some managers will try and excuse cases of sexual harassment as "just a bit of fun", especially at times like Valentine’s Day or at office parties, but they’re no fun for the person being harassed, and you shouldn’t be expected to just laugh it off if it continues. Behaviour of this sort is unacceptable, as well as unprofessional, particularly if people make it clear they don’t like it.