1) According to the Quran, Muslims cannot be friends with "unbelievers" so they cannot possibly integrate into British society as a group.
2) Sharia law directly opposes Western values. The death of apostates, the ban info homosexuality, the jizya tax for non-Muslims all contradict our values of tolerance, equality and freedom.
3) Muslms ultimately want the whole world to be Muslim and to live according to the rules of the Quran. They are allowed under the Quran to use violent methods to charge this.