The original link (at the bottom) is up and running again after being removed last night.
Just in case, here's the normal complaint form for you. And here's the main complaints page.
And this is my original post about the form for people who have been "impacted":
This is where you can have a first stab at lodging a claim against NatWest for costs incurred as a result of their payments meltdown.
If you click on the link at the bottom of their advice page, the form opens up.
NatWest claim form (Now this one is working again!)