Hi,
I know Peter has already commented and said 'yes' - Webb's, but I thought I'd add a little.
I have a bowl of the same shape, but with a green centre piece. I can't check the base or whether it's marked as it's packed away somewhere, but I never questioned it, either when I bought it, or since. Importantly, I have had other (cut) pieces using the same shape, and not always marked with a back stamp. It also features as a shape in contemporary articles on Hammond and Webbs.
Nigel