Since Howard has mentioned Edgeley concertinas, can I remind our OP Matthew - if he's still watching and hasn't completely lost the will to live - that these instruments are made in his home town. Edgeley's website displays both hybrids and traditional concertina-reeded models. I played one of Frank's hybrids a few years ago, and it seemed very good.

I've also been impressed by Morses, but there might be import duty to pay in that case. Of course we still don't know Matthew's budget, and these instruments may be out of his reach. Which is why I suggested that he contact someone like Robin Harrison if he's thinking of buying second-hand.