Answer:

This data is extremely difficult to capture and is not recorded in the HESA student administrative data records. Recent survey research carried out by the Association of University Language Centres identified a total of around 32,000 HE students on unaccredited language courses outside of their main studies (results based on 56 institutions surveyed in the UK, in 2007/8).

Date note:
Non-credit bearing course data used to be collected by HESA, but collection was complex and not all institutions filled in their returns undermining the reliability of the data. This is no longer collected and reported by HESA in the same way.

Data source:

The research was carried out by the Association of University Language Centres (AULC) looking into numbers and motivations of students taking a language as an extra-curricular activity, outside their studies.