I have always been quite pro Sentamu but frankly this strikes me as being plain silly, I am sure that this stunt is going to put Mugabe off his breakfast orange juice. I might join him by giving up wearing a vest, or maybe a bowler hat. It reminds me of the Irish Bishop who gave up wearing a mitre until young people returned to church, I think this particular prelate is still bear headed. If he decided to go barefooted, or to wear a hairshirt it might be more of sign.
Whilst we are on "clerical collars" by the way, there is really no such thing. What priests wear are "roman collars", a 19th century Roman fashion. Not only priests but Italian policemen (and women) and Italian soldiers still wear them, I think firemen/women do too. Basically they are worn under any garment that has a high stand-up collar. The "clerical collar" if there is such a thing is the black, purple, scarlet or white, in the case of the Pope piece, of fabric that goes around the neck, policemen etc, wear a colour that matches or contrasts with their uniform. The white linen thing was merely a hygenic thing to keep it clean. The French clergy, being less fastidious tended to wear collars with tabs the same colour as their cassocks until quite late. The German's have only started wearing them recently, most wore an ordinary white shirt with the collar covering the cassock collar, rather like the Fathers of the English Oratories, who not being altered at all by modern fashions hold onto the older Roman tradition.
It is for this reason that the Vatican has no problems with the efficient nine and ten year old boys who serve Mass early in the morning at St Peter's wearing them. I might put my servers in them.
Clerical dress is the cassock, but then that is really a university gown, again the Vatican seems happy to put anyone in one so even that is not solely clerical dress. I was amused to read that a new document on music by the American Bishops keeps say that the choir or the cantor shouldn't wear a cassock because it is "clerical dress", it advocates an alb which of course until thirty years ago was always regarded as the dress of "sacred minsters"that is sub-deacons and above, except of course in France but..........