Bob Bolton, one of my concertinas which you will certainly have heard is a G/D Salvation Army Lachenal Anglo, possibly originally in Ab/Eb.
(Not sure about the Bb/Eb in your post above, normal combination would be Bb/F). It is a high-quality instrument, regrettably the bellows is coming to the end of its natural life and something will have to be done soon about replacing it. (Dave Elliott advised at his Whitby workshop that they have gone beyond patch-up repairs).

I always found Alf Edwards' accompaniments a bit "thin", likewise for many other English players. In contrast, my late friend Joe Maley (who played professionally as "Jack Easy" on music hall and variety stages to the end of his life) could provide a rich harmonic accompaniment to any voice, any key on his visits to Fleetwood Folk Club in the late seventies. In his company I met a couple of Anglo players of similar age who could equal, in smoothness and musicality, Joe's playing on the English concertina. I regret I never got their names. They all learned to play in concertina bands in the twenties and thirties, and had a classical style far different from most players on the folk scene now.

It's very easy to overpower a singing voice with the concertina, but used sensitively it's possible, as Dick suggests, to do a lot more than single-line melodies or harmonies.

Ross