Can this kind of religious persecution really be going on in Britain today?

You use the word zealot. That reflects the truth of the matter. There are inter-religious marriages. Fanatical Muslims who follow the Sharia are in the minority. However, the Sharia (Islamic Law) states that a Muslim man who converts to another religion is to be killed, a woman will be imprisoned,. However, (presumably because women from whatever religion are expected to change their minds), if a Muslim woman returns to Islam she will be forgiven. The Sharia came after the Qur'an and does not reflect the teachings of Mohammed, any more than current Christian practice (Iraq/Afghanistan) reflects the teachings of Jesus.