If the choice is between breaking a promise or having a referundum , then break the promise, and then point out that an honest attempt had been made.

An  honest attempt was made to by forming a multi - partisan committee  (in which no Party had a majority, as what usually happens on committees) which could not get consensus, despite the fact that going in there was only one party, the Conservative party, who were against any change, For this committee to come back with a referendum is a disgrace.  For these Parliamentarians to shirk their responsibility  in such a blatant manner shows them no to be worthy of their position. Referendums is not part of a democracy.    Besides, what would  a referendum look like - six choices, 3 choices, yes or no and to what?