Tiscali is supposed to be dire. Unless they've improved things recently?
I'd suggest to stick with BT for your line rental/calls* & get broadband from O2 click here. If you're an O2 mobile customer (contract/PAYG), you get £5 off your bill each month. In addition, if you go via Quidco, you'll get a further £25 cashback click here, knocking a further £2 off your bill each month (in a sense anyway).
If you may save a lot more overall with other deals, but what's the service going to be like?
Virgin Media cable broadband & phone line click here (especially if you're in a fibre-optic enabled area) could be a good deal too, but may not be suitable if you're a heavy downloader especially during peak hours. Possible £65 cashback too click here.
Btw, I use or am a member of all the above & can recommend them all. G
P.S. Related O2 broadband forum discussions click here, click here, click here & click here
About cashback sites: click here, click here & click here
* Get cheap calls through your BT line by using click here & services like click here