Essentially, IR35 will affect all contractors who do not meet the Inland Revenue's definition of 'self employment'., Those contractors who fall under the IR35 rules will be liable to Schedule E taxation and National Insurance (N.I), following deductions for expenses. Income will be in the form of a 'deemed payment', following these deductions.
There has been a lot of debate recently over substitution clauses in agency contracts, and whether they do indeed defeat IR35. In this article I will sum up the Revenue's thinking toward the subject, quoting directly from their employment status manuals.