Hi all, this might sound silly, but I applied for a PhD place and just got an email congratulating me for getting an Mphil place. Is this because in England you first enrol onto an Mphil?

Yep, that's correct! Many universities in the UK enrol their PhD students on to an MPhil first, then at the end of your first year you can be upgraded to a PhD and head into your second year after successful completion of a first year report and viva.
Congratulations!