I was with PN for years for ADSL from a 20CN exchange but at some point the retention deals became dire ,didn't help that the exchange wasn't in a low cost area,anyway I migrated away to John Lewis BB which is provided by PN as the first year cost was cheaper than the last retention deal from PN plus I used TCB.
No change in the BB quality etc.other than the local exchange was upgraded 6 months ago so can now get ADSL2+ which improve things even if the exchange is far away.
Now able to get ADSL2+ Broadband