Marbled Thanks for your reply, I have just tested it without anything in the user context and user details and although sending and receiving calls works OK, the issue remains the same.
Sip show peers for the trunk is
Name/username Host Dyn Forcerport Comedia ACL Port Status Description
Engin 08XXXXXXXX 203.161.160.71 Yes Yes 5060 Unmonitored
11 sip peers [Monitored: 4 online, 6 offline Unmonitored: 1 online, 0 offline]