Mozz, registrars do not attend ceremonies conducted at unlicensed premises, eg private homes. Whilst the marriage would be regarded as legal in countries that recognise Sharia law, Malala has been married in this country in a Muslim ceremony - as very many Muslims are - which means that she and thousands/millions like her are not legally married in British law and are, hence, unprotected by British law. For example, should the marriage fail, she cannot seek divorce through legal channels - only through a Sharia court - where her rights do not equal those of her spouse and where she will very likely be told to go home, behave herself and obey her husband.
I admire Malala and have supported her quest to encourage education for women since the beginning. She was like a breath of fresh air. This, however, disappoints me, in that whilst I thought she really was running with the ball, unless she crosses the 'Ts' and dots the 'Is' to ensure that her marriage is legally recognised here, she will not only have dropped the ball - she will have left the field entirely. A marriage conducted under Sharia law is not conducive to the advancement of the education of women. Quite the opposite.