hi - you don't explain why you're 'guessing' Nazeing, so unsure if you have Geoff. Timblerlake's book or not. I'm with you for Nazeing on the shape, but it's the colour that's giving the problem plus the bubble intensity doesn't look strong enough. However, you learn in this game never to say never

They were known for their swirling bubbles, and I can't really see that in this piece, although the colour may be preventing a good image, and in the book their lilacs and purple don't generally appear anywhere near as dense or dark as this one.
W/Fs certainly did a shape similar to this, but theirs wasn't bubbled or swirly - just a dense solid colour, and with a ring to die for (as with many of their thin pieces). Having a good quality ground and polished pontil depression is not remotely exclusive to W/Fs - many factories produced pieces with such a feature - some of them British too

If this is neither then regret that's the limit of my knowledge on unmarked purple pieces.
