> Is your Sipgate account a non-UK (German or Austrian) one..? If so you
> need to dial the number using the full number in international format, the
> SIP ID on its own won't work. Try 0044 20 7043 1320.

Ivor, a U.K. account, I have it setup to dial 020 7043 1320, which
according to sipgate docs should work

I tried it on two different accounts, it appears to get connected, but
nothing is coming through

If I check the sipgate website for calls made, I see

25/10 20:39h unknown unknown

If I call from my first account to my second account, it completes
correctly back to my Asterisk box, so it can't be that