OK. Took a gamble after not getting any replies here and none helpful replies on CN and just kept unscrewing the Silver focus rotation ring and could see the focuser section coming away from the main refractor tube. So it seems a simple connection.
https://c1.staticflickr.com/1/426/31...ca41f5_z_d.jpg
The bad news - I wasn't able to tell the OD/ID as I don't have a pair of calipers, and I don't have any pitch gauge guides to tell the pitch/thread type. And I'm strongly suspecting that it's a proprietary non standard type too, so I'm starting to think that getting a replacement focuser isn't probably gonna be doable. Just my luck.
Dave