Connect using Ethernet cable and see how that goes. This will determine whether or not it's local wireless or Internet connectivity.
If you still have issues then it's likely to be Internet or the router. I assume that Talk Talk provide the router, so if you still have issues with Ethernet cabling, then you can claim it's not wireless and tell them to look into it more.
Also, if you're still having problems after the Ethernet test, you could also try using a replacement microfilter. Routers usually ship with at least 2 of these.