I would not trust anything that BT says as far as end of copper line is concerned. My experience of BT is that a lot of their engineers will pass the buck on ADSL faults, after all its just like any technical thingy, unless you get the "cream of the crop" engineers you aint going to get the result you were hoping for. Easier to blame hardware or customers equipment.
Our experiences of Linksys routers/wireless networks have been nothing short of useless. They overheat if let sitting flat. We have installed all sorts of ADSL equipment from Zyxel, Cisco, Draytek, Linksys, 3com, Dlink, Netgear, dynalink, and others.
I have to say the most reliable and configurable of the lot is the Netgear DG834G version2 which ..... DA DA..... uses the chip and we never get any problems. In fact it is one of the best routers for holding onto low SNR we find.
One can only assume that their are outside influences at work. Does'nt BT normally supply crippled speedtouch routers. Personally I reckon the router market is pushing suppliers to supply lockin routers in turn for a big fat pay back, bit like life insurance companies do for finiancial advisers.
Oh, and finally one peice of advice, if your router is a netgear install it on its side in an area with lots of airspace. And generally if your ADSL router does get hot you may get frequent lockups or dropouts. Stands to reason really electronics dont like getting really hot. HTH someone.
And yes, I have to agree with Jude, checkout your ISP and make sure you are not suffering a ISP dropout. First thing check your router stats and see if you got sync. Probably may well be saturation of ISP network. Basically if you have Sync, means you got ATM over BT ADSL network. No IP, or roter not connecting to your ISP then its an ISP problem.
Couple of useful tools.
speedtester.bt.com see http://www.kitz.co.uk/adsl/btwspeedtest.htm
Dial 17070, press option 2 listen for pops, clicks or noisy/buzzy line.