However, it was clearly stated numerous times by Her Majesty's Government in the lead up to the referendum that it would treat the referendum as definitive and a promise was made to the electorate that Parliament would give effect to their will as expressed through the Referendum.
The Leader of Her Majesty's Loyal Opposition also made a commitment to do this.
If Parliament does not deliver on these commitments, it will be the greatest failure of Parliamentary government in the United Kingdom since 1689 (since before there was a United Kingdom.
They are not constitutionally bound to do so. But it will still be a failure of government.
It would be a little different if this was a deliberate decision - if a strong Prime Minister had stood up and said "We're not going to do this." But it's happened because the Prime Minister is weak - and also because she made the monumentally stupid decision to throw away the outright majority the government had by calling an early election in 2017.
What, pray tell, are they bound by?