Here is an 'official' guide to what is required in a Modern Slavery Statement|Most organisations don't need to produce one by law (it's for larger turnover companies) but understanding the principles is important for all organisations.
Getting up to speed on Modern Slavery - how to recognise it, the due diligence processes you need to carry out and even the training for staff to help them recognise it.
SSN's tips for users
It's important that all organisations are aware of the risks relating to modern slavery, so a basic working knowledge is essential, even if in depth audits and annual reports aren't necessary.
Having said this, your organisation should consider making a positive statement about modern slavery and how you intend to guard against it and raise awareness of the issue. This may be of particular relevance to certain kinds of business activity where modern slavery (e.g. through people trafficking) might arise.