Hi all - I think I may have stumbled on the solution: the problem is the Huawei hg556a which does not seem to allow devices to talk correctly around the network. The fix which seems to work (for me) is to set-up both printer and all PCs, iPhones, iPads etc with fixed IPs. You need to set the IP on both the router and the devices (including the printer which in my case is a HP Officejet Pro 8600 Plus).
To do this on the router navigate to 192.168.0.1 (or other as per instructions) and enter using the standard user / password which for me is user:vodafone and psswd:vodafone. Go to the Router menu option, then LAN and enter your devices. On the 8600 printer it is very easy to set the fixed IP via the control panel on the printer, other printers may require you to do this via their network access portal using their IP address. On the iPhone/iPad etc you just need to enter into WIFI options and press on the small blue arrow of the network you are connected to and then enter the correct Static IP data which for me is:
IP Address - 192.168.0.197
Subnet Mask - 255.255.255.0
Router - 192.168.0.1
DNS - 192.168.0.1, 192.168.0.1
Seach Domains - localdomain
Above addresses will vary dependent on the IP address you have given the device on the router (obviously) and also the router's IP address (which I think in some countries is 192.168.1.1
This also solved an issue I had printing from a Windows based laptop using VPN.
Hope this works for you all too.
Niel