This behaviour is sexual harassment and you do not have to put up with it.
The first step is to make it clear to your employer that you do not like the behaviour and you want it to stop. Ask your union rep or HR to help you with this.
All organisations should have zero tolerance of sexual harassment. Your employer should have a specific policy in place outlawing the behaviour and explaining how you can pursue your complaint. Get hold of a copy and discuss it with your union rep.
If the social event is work-related – for example, an office lunch, client dinner or office party – your employer will be liable for your boss's sexual harassment. Your boss will also be personally liable as an employee.
And even if the advances take place at an event that is not work-related, there will still be unlawful sexual harassment if your boss penalises you for rejecting his advances. This is because under the Equality Act, it is sexual harassment to treat someone less favourably than they would have been treated had they not accepted or rejected conduct of a sexual nature. For example, if your boss asks you on a date and you refuse and this contributes to you being overlooked for promotion, this will be unlawful sexual harassment.
Keep hold of any evidence of the behaviour, such as text messages, emails, screengrabs of online postings and so on, in case it is denied.
Your boss's threat to end your promotion chances is a clear breach of the ban on sexual harassment contained in the Equality Act 2010. If you are not a union member, you can get advice from the Equality Advisory and Support Service, Acas or Citizens Advice.
If you are thinking about a tribunal claim, be aware that time limits are very short – just three months.
For general information on bringing a tribunal claim, including information about Acas early conciliation, see our section on Enforcing your Rights.