From Hansard...
hansard.parliament.uk/Commons/2016-02-25/debates/16022537000001/EuropeanAffairs
Column 497, Hammond:
“Let me be clear; the Government will respect the outcome of the referendum, whatever the result. There will be no second referendum. The propositions on the ballot paper are clear, and I want to be equally clear today. Leave means leave, and a vote to leave will trigger a notice under article 50. To do otherwise in the event of a vote to leave would represent a complete disregard of the will of the people. No individual, no matter how charismatic or prominent, has the right or the power to redefine unilaterally the meaning of the question on the ballot paper.”
“A vote to leave would trigger a fixed two-year time period under the treaty for the UK to negotiate the terms of our exit from, and our future relationship with, the EU.”
Column 498, after Salmond had asked:
“Before notification was given under article 50, given that the referendum is an advisory one in terms of the constitution, would there be a vote in Parliament?”
“The Government’s position is that the referendum is an advisory one, but the Government will regard themselves as being bound by the decision of the referendum and will proceed with serving an article 50 notice.”
If the MPs had wanted a vote after the referendum they could have tabled a motion to have that included in the legislation, they didn't.