Thanks for posting this, Mr. And I see they've used my book The Mood Modern as part of their research. I'm flattered!
I haven't yet read the article, but in response to Nidostar's comment about what had originally caused the British Musicians' Union to instigate its embargo on library sessions, it's very simple.
Until ca. 1951, British libraries had an agreement in place with the MU, which allowed them to recorded in England, hence, for example, all the Chappell sessions that were done in London. Then the MU, which had always been anti recorded music, decided that library music would eventually put its members out of work, hence the introduction of the embargo, which lasted until around 1961, when several British libraries came to an agreement with the MU, but under a very strict set of rules. Understandably, the libraries involved quickly grew tired of those restrictions, 'broke' them, and the embargo resumed until July 1978, when it was lifted thanks to the joint efforts of Robin Phillips of Bruton Music, and Peter Cox of KPM, who'd opened up negotiations with the MU the previous year.
Throughout the 1950s, '60s, and '70s, the Musicians’ Union's journal, Musician, regularly carried a list of companies for which its members were not allowed to record - naturally, those lists included the libraries - along with a warning that any members who did choose to record for said companies would be thrown out of the Union. I don't believe that ever happened, though, given the great number of 'phantom' library sessions that took place in London during that era, and the London sessions guys who quite rightly went abroad to record for various British libraries.
I'm certain about the above because I read it all in the pages of Musician, and in other very reliable sources, like the journal of the Robert Farnon Society, Journal into Melody. Moreover, I had the privilege of interviewing the (now sadly late) Patrick Howgill as part of my research for The Mood Modern. Patrick had set up the Keith Prowse library in 1956, and he recalled for me, in fascinating detail I might add, the above circumstances. And in March 1980, during his interview with Philip Tagg, Robin Phillips said the same of the standoff between the MU and the British libraries.