I have solved that problem.
It was to do with the STUN settings (only tick the STUN box and none of the other in network setup).
I have also got remote extensions working perfectly - either over VPN, or directrly from the internet.
Only have one remaining now
I have 3 'standard' phone extensions.
1 connected to a Granstream HanyTome 486 adapter - works fine.
2 connected to a Netgear TA612V adapter - works fine EXCEPT for calls to/from Sipgate - I hear no sound from other party, they can hear me. - The other Sip providers (and Uplink to Skype) work fine - just Sipgate on this Adapter