Until just now I'd never heard anything by The Spectrum other than the Captain Scarlet theme...and had no idea they even were an actual group. Even when I was seven or eight years old, when I saw "The Spectrum" listed in the closing credits I assumed it must be a kind of joke; that these were singers brought in by Barry Gray and given a made up name, because the name seemed too on the nose to be real. I'm glad to learn I was wrong, and I'm going to call this a lost gem. I'll definitely be listening to the rest of their work now!
I know what you mean Richard. They were far more prolific than I ever thought. Check out You Tube, there's loads of their singles on there - more than I've posted - and maybe even an album. I wonder what happened to them?