At what stage of the recruitment process should employers make the decision to take positive action?

According to government guidance (Equality Act 2010: A quick start guide to using positive action in recruitment and promotion), positive action can be taken at any stage of the recruitment or promotion process. The guide gives the example of the positive action provisions being used to complete a shortlist of candidates to go through to the next stage of assessment. However, the guide goes on to say that it is expected that positive action will mainly be used as a tie-breaker between candidates of equal merit for a particular post at the end of the recruitment process, ie at the decision stage. By then, the employer concerned should have been able to establish all of the relevant factors to enable it to determine, as definitively as possible, whether or not the final candidates are truly as qualified as each other.