Hello,
These dishes/ash trays are currently regarded as being Nazeing (no 'K'). You are unlikely to find any reference that includes them at this point in time, although there is Geoff Timberlake's book "75 Years of Diverse Glass-making to the World" for a detailed history of the company, the known catalogue and a selection of photos. The pontil mark is just that and not some sort of seal. Possibly broken and then finished using heat to get that effect - Adam?
There is a little more information about Nazeing on my site (see below). Look via 'Glass to buy', then 'English', then 'Nazeing'.
Nigel