Getting Married in UK. Waiting period

My partner already has a fiancee visa to get married in the UK. I am planning to get married in England.
I understand there is a 28 day waiting period to get married once a notice is given. Would I be violating any law if I have a religious ceremony (unofficial ) before the 28 days and have the official civil ceremony at the registrar office after the 28 days?

Assuming the religious ceremony isn't recognised as a legal marriage under British law (in a mosque for example), then there would be no problem.