Despite the opening comments, the link says that the Home Office refused to comment.

A quote from the link:
The school is part of the Lincoln College Group, which is no longer allowed to sponsor their international student visas after being rated as requiring improvement by Ofsted in August last year.

The four students are affected because diplomas from the violin-making school do not have wider educational recognition from Ofsted, despite the fact they are regarded around the world as a benchmark of professional quality.