According to the Roobarb Forum today 27/05/19 The following information was posted. I am quoting exactly what was publishing on the forum. I take no credit for this information. I am simply passing on what was posted.

Thanks to the help of Mark Aldridge, a master version of this TVS one-off has now been returned from the USA. Despite being freely available on NTSC VHS many years ago, the master tape was destroyed by Disney in 2010.

Mark Aldridge is an expert on Agatha Christie and he remarks:

“First shown in 1986 and shot on 35mm for TVS, Murder by the Book is a rare example of the Agatha Christie estate allowing a production to present a fictionalised version of the author. Christie's daughter and grandson, Rosalind Hicks and Mathew Prichard, were so impressed with Nick Evans' script (and the film's connections with the South Bank Show) that they consented to the depiction of Christie and her detective Hercule Poirot for a fee of just £1. In 1990 it was shown in the United States as part of the commemorations for the Agatha Christie centenary, where it was also released on LaserDisc and VHS.

I thank Scott Wallace Baker, a Christie megafan who casually mentioned that he knew there had been a laserdisc release, leading to this discovery.”