Many thanks to all - excellent advice & suggestions!
Installed adblocker on IE and Chrome but the PSB appeared on AOL (Browser?) so I wondered if there was a way to disable the AOL browser, couldn't see anything on google? Pretty sure there's no adblock for AOL.
When you enter PSB.com in the AOL pop-up blocker all that happens is that the PSB page pops up blank. Just now PSB is absent but it has a habit of creeping in. The only short-term thing you can do is reduce it and drag it to the edge of the screen.
Am in south London (UK). Will investigate those other ISPs with thanks,