Yes they will mate, I'll be wearing my hoodie and Maggie Thatcher mask!
Nah, you'll get arrested by Gwent Police at the toll booths! Those guys actively look for something to do. They tried to book me for speeding in the 50 m.p.h. zone at Plaza Rogiet, just before the toll booths, only I wasn't speeding at all (long story, but I challenged it and was able to prove my innocence, took 3 months of legalise letters back & forth mind you).
You wanna don a Welsh Rugby Shirt ready for Saturday's game. It won't save you the £5.70 toll fee, but at least they'll let you through!
...Oh, and go on the old bridge if it's open. It's what us locals use. Nearly always quicker & quieter and the booth staff will actually smile (they are grumpy sods on the new bridge).
Bon voyage!