Oh yes, that is unforgettable indeed. Yet I recall there were loads of reviews on the website at the time raving about the garment.
Poor old Twiggy now seems to be on in-store posters (looking a touch haggard) for the 'mainline' M and S Woman range, so perhaps has escaped from Per Una. The question remains 'who exactly is Per Una aimed at???'
As far as I'm concerned Autograph Weekend is about the only M and S 'brand' worth checking out regularly for wearable stuff.