That promise was not in any way made by Farage, it was made by Boris Johnson and co.[1] [2] I don't like Farage, and I hate the leave vote, but his criticism of it was honest given that he was definitely not the one who made the promise.

For what is worth, he was criticising them (though not sure about this specific point) from before.[3]

1. http://leftfootforward.org/2016/05/boris-johnsons-brexit-bus...

2. http://www.dailymail.co.uk/news/article-3584627/The-Boris-bl...

3.http://www.politico.eu/article/nigel-farage-ukip-leader-vote...