Well, it's been overwhelming, and incredibly interesting and thought-provoking. Thank you all for taking the time and trouble to respond. I've now been pointed in the direction of the following site, entirely devoted to VMC (www.librarything.com/groups/viragomodernclassics), which is definitely worth looking at, in case you haven't already discovered it. I've also asked the current editor of VMC to look at your comments, and hopefully she will take note of the following: that the dark green covers are missed, and that a number of much-loved books have been allowed to go out of print. Certainly, it seems a shame that May Sinclair's novels have lapsed into the void, though I am hoping to track down some second hand copies. And I'm determined to find a copy of "The Brontes Went To Woolworths".
I'm not sure quite why, but this subject has also sent me off in another direction -- back to one of my favourite childhood authors, E. Nesbit. I've still got my Puffin editions of "Five Children and It", "The Wouldbegoods" and "The Story of the Amulet". But I hadn't realised that she also wrote ghost stories. Has anyone read them?