The BT Wholesale situation seems to be deteriorating. Basically, the units are required to be internally seperated so BT Retail has no unfair competitive advantage on service grounds. But ultimately they are not accountable to anyone, and shielded from angry customers by this setup.
My father-in-law has been waited three weeks for BT Wholesale to do some rewiring to get him broadband. All the ISP (plus.net, who I do recommend for browsing and email, not p2p and gaming) can do is call every 2 days to be told nothing has happened; please chase us again in 48 hour.
flyclub, I'm no expert on these things, but searching for and then manually entering BT's DNS server IP addresses in your connection settings may help.