Are Muslims carrying banners crying ' death to the infidel ' committing treason ?

There is a logic to this question. The Queen is the head of state in Britain. She is also the head of the Church of England if I recollect correctly. Therefore by definition she must be an unbeliever in Islamic terms and by default must be an infidel. So surely a Muslim carrying a banner as described in the question must be committing treason by indirectly calling for the possible demise of our head of state. If I remember correctly treason still carries the death penalty in this country ( technically ). Why has this never been tested in court ?