The URL for online banking in case it's the Natwest top page that's the problem is:
https://www.nwolb.com/
and in case DNS related can be accessed via it's IP address as:
https://155.136.72.107
Hope this helps.
Alternatively I'd ask are you using a proxy? If not then try one. If yes stop. But turning on my cache gets pages telling me to turn off the proxy cache settings.... maybe that's the problem. My old proxy cache had the address 80.5.160.7.
Rob