What a great find! This is the original version of Jobling's 11600 'Open Footed Vase'. This type with the skeletal legs proved hard to remove from the mould and was prone to damage, so the base was re-designed with a more conventional round foot.
As far as I'm aware, the modification was made soon after the vase was introduced, hence these original style versions are quite rare.
The registration number should read 796181 - this corresponds to a registration date of 6th September 1934. Not all have the full number. I have been lucky enough to find two of these early examples, one in blue (for which I had to pay a lot!) which has the number and one in pink which has a moulded 'Regn. Applied For' mark. Interestingly the base finish is different on both of mine, the pink one has been ground and polished, while the blue has just had a light fire-polish. Your vase looks to be finished in the same way as my blue one.
There is another vase in a very similar style to this, but it is now believed not to be by Jobling (they turn up in some very un-Joblingy colours and although the pattern is similar the mould details are quite different. In the past I had mistakenly thought they were Jobling and stated as such, hence the confusion). An example appeared on this board a while ago, and Pamela has one on her site here: http://pressglas-pavillon.de/vasen/08008.html