qgis - Joining postcodes to coordinates in a .csv file

I have a .csv of land registry sales data that includes full addresses and postcodes.

I'm trying to geocode all the data so that I can plot it in QGIS but my issue is that I have 2 million records that I'm not sure I can feasibly run through any commercial geocoders without paying heaps (if anybody has any ideas let me know)

Instead I've downloaded Ordinance Survey's code point dataset which lists coordinates for all of the postcodes in Britain. I'm hoping that there is some way that I can join those records with those in my landreg dataset so that I can have some degree of accuracy in plotting my points.

Any idea on how to do it?