[eponymous1212]

Thank you all for your various explanations and points of view (the finer points of which are out of my depth). What I am able to clarify is:

1. It is definitely a switch
2. Right at the outset Matt picked up that it was “my actual ISP issued IP address, the address your cable modem gets” that was being detected.
3. The switch is fully automatic with no scope for configuration
4. To all intents and purposes I purchased the wrong piece of kit and thank you for enabling me to discover this.

The issue now is to avoid making the same mistake again.

- Is a manual switch box also an option or would I encounter precisely the same problem?
- Could you please suggest any basic routers that are likely to fit the bill?

Thanks again for all your help.
Eponymous1212