Valerysthal made this and most likely, also Portieux, their sister company. It appears in an old V catalog. I see you are in London, so this is most likely an original that did not wander far from where it was made (relatively speaking). However, if I found this in the USA, my first thought would be to see if it is a Westmoreland product, as Westmoreland copied it. That mold later ended up with Summit glass co., which made it in a variety of colors (as did westmoreland). There are subtle differences in size between the original and Valerysthal, and I am not up on my milk glass -- will let the experts in that field ask the questions regarding size, shape, what it has or doesnt have. At least I gave you a direction. there is a milk glass website that might be able to give you more info. just do a google search for national milk glass collectors society.
regards
mr. vaseline glass