HMRC has recently published answers to 13 common questions asked about the NIC treatment regarding the complex rules surrounding disguised remuneration. The legislation was introduced to prevent employers from avoiding or deferring paying income tax or NIC on such remuneration paid to employees in the form of such things as loans and trusts, including employment benefit trusts (EBTs). These are the type of structures that have commonly been used by promoters of tax avoidance schemes aimed at contractors to circumvent IR35 and retain a greater percentage of a freelancer's income.
The guidance which can be found via HMRC website (PDF) explains how the NIC legislation, which took effect from 6th December 2011, works, how earnings are measured and how employers who have employed EBT's and similar arrangements can settle outstanding tax enquiries.
Draft legislation on disguised remuneration that was published in December 2010 attracted criticism due to its complexity and its capacity to ensnare unintended arrangements. In response, the government published draft guidance last year to attempt to clarify how the legislation will work in a number of given scenarios, including how normal dividend payments following a share transaction will not be caught.
Please link to the document rather than just the hmrc website root