see url: http://www.bbc.co.uk/news/uk-politics-40555639
Apparently, whether an alleged racist remark is acted on by a Prime Minister, depends on how weak that Prime Minister feels in regard to her continuing her job as Prime Minister. A Prime Minister who criticizes a Leader of the Opposition and Members of his political party for making alleged Anti-Jewish, or anti-Semitic remarks, such as "I support the Palestine Cause", or alludes to the Haavara Agreement of 1933,
see url: https://en.wikipedia.org/wiki/Haavara_Agreement
cannot stand by and allow such comment to be made, by one of her own members, because it may jeopardize her support amongst the people, and lose her party a future election, by removing her right to criticise the other party for using them, else she will be accused of supporting and condoning racialism herself or using double standards regarding others; and of being a hypocrite!
It appears that the use of the phrase has less to do with with stopping racism against ethnic citizens and their offspring who originally came from Africa, and upholding their rights not to be discriminated against because they have a dark skin, and more to do with the current political state of the parties which are dominated by their native elite citizenries, whose skin is of a lighter shade.
Origins of the phrase:
see url: https://en.wikipedia.org/wiki/Nigger_in_the_woodpile
I can't see the racism, or the phrase being derogatory at all, though I don't advise anyone to make a habit of using it, in case they are misunderstood or misinterpreted; or if they do, make sure that they know how and when they may do so...at their peril. Living in a post modern, late capitalist, society where fake news, and untruths have become the norm, has jeopardised ones rights of free speech.
Once again, we are in the chains of the politically correct, lighter and paler skinned native elite. I dare say, that the vast majority of our African ethnic citizens, mostly ignore it as irrelevant, or look at its utterance in such a trite way, as more a mere storm in a teacup, and its use a completely futile gesture, which does not even come close to achieving equal opportunities between the various ethnic minorities, who live in our country or on our planet. Personally, I wouldn't use the phrase, or recommend it even; unless I was in the company of an ethnic friend of African origin, whom I knew very well, could take it as a joke, realise I wasn't being abusive; wasn't being offensive; and whom I knew wasn't going to punch me on the nose... But politicians never learn, because they are so superior to the rest of us...
Just a thought,