Just a quick update with more info.
When the red light starts flashing, try to connect to the routers web interface. If you can do that then you know it's not that the whole router has rebooted and it is just a connection issue. If you can still connect to the router, then it's rare that it's actually a router problem - not unheard of but rare! On the flip side, there is no good reason that the router should be rebooting, unless it's faulty or there is something else happening within its environment that is somehow interfering with it (this is the old water pumps, fish tanks, small-bore plumbing pump, or large industrial loads coming online thing). If the router is rebooting and there is no good reason, it may be faulty.
Regards just getting a router and plugging it into the modem/router that you have; the Vodafone device doesn't have the settings to be stepped down to working as just a modem. Even if you turn off it's DHCP functions, it'll still provide many of the hidden network services that a router provides, and adding in a second router can create all kinds of problems. It's very much the VF modem router or replace everything (you can actually use a third party modem with the VF modem/router, but again it's undocumented and unsupported).
So, see if you can still log into the router when the red light is flashing. I'm suspecting if you talk to VF they may want to send you a new router. If you go down the route of getting 3rd party equipment, come back to these boards and there are several people who can help you!
