Cheers Christine and David,
Thanks for your help. The thickness of the glass is about 3mm. I bought this bowl along with a lidded cup, again for the Society of Glass Technology, London Section , many years ago and forgot all about them until I found them after a spot of reluctant Spring cleaning. The lidded cup is made for an annual dinner in January of the following year and seems to be a type of Pyrex.
I hope one day someone might be able to recognise the blowers or even the glassworks from the darkness of the photo ....you never know with the internet . :X: It would be fun to find out !
Here's a pic of the cup.