h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I was amazed to find a transcript of this broadcast. Where on earth did it come from? The only way I know to access past radio scripts is to go to BBC Caversham, and then it's likely to be on a microfilm reader, which I hate. Maybe they've been (re)transferred to computer access now, which would be preferable.
I only learned of the programme quite recently, from a Paul Temple website, and I got hold of the cast from the 'Programmes-as-Broadcast' records. The cast I have gives Marmaduke (assuming that he is the servant) played by Lester Mudditt, rather than Malcolm Hayes. Lester Mudditt played Paul Temple's Sir Graham over many years.
The script owes something to what was then called 'Ten Little Niggers'. But it defies analysis; it is just a fun idea to bring the 'immortals' together.
Interestingly it was written by Edward J.Mason (then of Dick Barton, of course). Had he done it a handful of years later, I am sure he would have included Dan and Doris Archer, whom he was to write about for so long.