Don't know about leads, how about vague thoughts

I remember this from December, but since I shy away from these swirly bubbled things, can't recall what I thought at the time. Amazing how images can mislead - I'd have put money on this being taller than 2.5", Don't know if you have Geoff. Timberlake's book, but there is a pic. of a yellow posy which looks similar to yours, with this massive everted downturned rim, but I can't make out if the book example is clear cased at the base like yours. Certainly the yellow looks about right, even down to the blotchy effect where the colour is more concentrated. Unfortunately, the book doesn't give dimensions - neither do I know what the pontil mark area looks like on the Nazeing piece.
I even wondered, briefly, if yours might have been Alum Bay. Have you looked at many 'yellowish' Nazeing posy vases.
I don't think the direction of swirl would discount this being Nazeing. I wonder if it might by any chance be R.B./S & W.
Sorry it's not much help m.