You may be initially enrolled for an MPhil in the first stage of a PhD programme. You’ll then ‘upgrade’ to PhD registration, usually after one year, once your research has progressed. In some universities, you may be asked to pass a viva before proceeding to PhD. Enrolling for an Mphil/Phd is perfectly normal in the UK. Most PhD programmes have the Mphil element at the beginning of the PhD programme but you can study MPhil on its own although it is uncommon.
You can read more about the difference between MPhil and PhD.