In April 2002 the (then) Department of Trade and Industry (DTI) published a 24-page booklet entitled “A User’s Guide to late payment legislation: The Late Payment of Commercial Debts (Interest) Act 1998, as amended and supplemented by the Late Payment of Commercial Debts Regulations 2002.”
The legislation has changed since the guide was published. You can read the guide here. It is important that you note, however, that the guide does not fully reflect the current legislation.