Let's face it: it's B.S., and the Manchester Museum will uncover them again! If in the XIXth century puritans didn't prevent people from bringing mummies from Egypt and displaying them (including unwrapping dinner parties), would they be able to do it in the XXI century? NO!
Check out the blog and the comments in the above link and check also round-the-world news about it:
BBC - Egyptian mummies at Manchester Museum have been covered up after complaints from a small number of visitors http://news.bbc.co.uk/1/hi/england/manchester/7413654.stm
Times - Museum covers mummies' modesty after surge of complaints by visitors http://entertainment.timesonline.co.uk/tol/arts_and_entertainment/visual_arts/article3981425.ece
Telegraph - 'Naked' mummies covered after complaints http://www.telegraph.co.uk/news/uknews/2000248/%27Naked%27-mummies-covered-after-complaints.html
Daily Mail - Fury as museum bosses cover up naked Egyptian mummies to protect 'sensitivities' of visitors http://www.dailymail.co.uk/news/article-1020891/Fury-museum-bosses-cover-naked-Egyptian-mummies-protect-sensitivities-visitors.html