Thank you for both of the suggestions. I have encountered another problem:
I have a Huawei E3131 USB stick which I am trying to use with a Zyxel VMG8924-B10A router.
When I connect the stick to my laptop it generates a web page and I have to click 'Connect' to establish a connection. Ok when I am using the laptop.
If I connect the USB stick to the router, the 3G connection is activated if the DSL line is disconnected. But if you then try to access the internet via the router you still end up with a web page where you have to click 'Connect'. OK if you are on site but a bit of a problem if you are not there and want to establish a remote connection when the DSL connection is down.
Do all sticks work like this?