This is what the co-Vice Chair of the Chakrabarti inquiry, Professor David Feldman, said about the Macpherson principle, in his January 2015 sub-report to the All-Party Parliamentary Group Against Antisemitism, chaired by John Mann:
It is sometimes suggested that when Jews perceive an utterance or action to be anti-Semitic that this is how it should be described. In the UK this claim looks for support to the 1999 Stephen Lawrence Inquiry, written by Lord Macpherson of Cluny. There Macpherson wrote that ‘a racist incident’ is ‘any incident which is perceived to be racist by the victim or any other person.’ If we look at the context in which this quotation appears, it is unambiguously clear that Macpherson intended to propose that such racist incidents require investigation. He did not mean to imply that such incidents are necessarily racist. However, Macpherson’s report has been misinterpreted and misapplied in precisely this way. Its authority has been thrown behind the view that such incidents should, by definition, be regarded as racist. In short, a definition of antisemitism which takes Jews’ feelings and perceptions as its starting point and which looks to the Macpherson report for authority is built on weak foundations.