OK, like some evidence like this:
View media item 3340
Looking at the numbers on the table between London and the West Midlands/North West there's now about 10 million (as the figures are in thousands) extra trips being made every year.
That's about 27,000 extra a day, filling an extra 39 trains (assuming 100% seat occupancy) with 429 coaches between them.
That doesn't even allow for Scotland or North Wales, which although have seen smaller and are split over more than one route would only add to those problems.
Based on that can you start to understand why adding a few extra coaches and a few extra trains here and there isn't going to cut it when trying to provide the capacity needed.
It's why those who have looked at the information are more and more thinking, "you know what we do need HS2, or at least something very much like it".
HS2 is far from perfect, but what other option is there? Even if there is one it's probably too late to start design work on it to be able to deliver it within the timeframe.