Same here guys, fortunately I'm in a position to go to my local branch and get some cash if I need it. I too phoned the bank just to check it wasn't their fault, I was ready to throw a wobbly at the JPAC guys.
Just spoke to Nationwide, you can go into your bank and withdraw money, no mention of amount though. The bank are able to see how much you are due to be paid so that shouldn't be an issue with them.
They also said they will refund any charges incurred as a result of the mistake.
Be aware though, most Nationwide branches are closing at 1500 today so be quick.