David,
There is also clearly no majority of brexit supporters in Parliament.

….and never has been. They are the establishment ruling elite.
If they continue to subvert the expressed will of the people a populist party is likely to emerge again and threaten their position as UKIP did.

Dave,
They will not even tell you what the benefits may be.

They have told you. It was all laid out in the Leave campaign. Nothing has changed.

It merged in yesterday's questions that Corbyn called for article 50 to be triggered immediately after the referendum result came in. Just like Cameron did before.