A constitutional expert raised an interesting point. Leaving the EU could be unconstitutional. While the referendum asked if we wanted to leave, the method of leaving wasn't covered at all. Meaning there is no mandate on how we should leave. Literally Parliment have no authority to choose or negotiate how we leave.
All of this confirms that the people who asked the question had just assumed that we'd vote Remain. They actually weren't thinking what would happen if we voted to Leave, and what we'd need to do and what authorities they'd need to achieve it.
Business Insider UK: This is how politicians could block Brexit, according to a constitutional expert