I am at secular school in U.K. It is compulsory to attend secular school.

Answer

The right action is to simply walk out of class and perform Asr Salaat wherever place is available. Then if they want to expel you, make Shukr to Allah Ta'ala for the expulsion.

Is there no Muslim school where you could study? It is the Waajib obligation of the Ulama in U.K. to take up this issue with the government, and if necessary to institute court action against the school for suppressing your religious right.