The Burqa is not in the Qu'ran but that does not mean it is not for some Muslims a religious requirement.
Praying 5 times a day is not in the Qu'ran yet it is fundamental to Islam ... These are all mentioned in hadiths and other texts that is not in the Qu'ran
Christians have many traditions which are not specifically in the Bible but are traditions as do many other faiths. That does not detract from its religious importance for individuals.
I'm surprised there is apparently "enthusiastic backing" in UK for this ban. I thought the British had more sense than that especially seeing such a tiny amount of Muslim women actually wear it.