These were at the cheaper end of the market, so you are probably looking at a lesser Stourbridge name, or Burtles Tate. I'm sitting on a few adverts from this era and there were a number of firms making items like this, I don't believe it is possible to assign them. Density can be variable as well due to chemical mix, but if it's English I would expect in the range of 3g/cc to 3.3g/cc