DMcG,
Now, is any leaver prepared to admit they might be wrong and Brexit could turn out to be one of the worst things Britain has ever done?

Of course, and I believe I have said that in my own words, but I am strongly of the opinion that even though there will be costs, it is the best option for the long term benefit of this country.

Only history can decide who is right.
Until we have left there is no way of knowing.
As of now we do not even know what the deal will be, so let's not be abusive to people just for holding a different opinion.

all the data in it can (such as forecasts and analyses and statements from businesses and other governments)

Forecasts and analysis of what? We do not have a deal to analyse yet!