And the government is the representative of parliament in negotiations.
The fault is of the UK governments that it didn’t and doesn’t get the parliament’s blessings before negotiating.
The previous 2 years was a waste and therefore, unless Boris can prove any deal he makes will pass through a parliament that loathes him, any potential deal he will propose (he hasn’t proposed one yet) will also be a waste.
Perhaps parliament should negotiate with the EU then?
Boris and a few other Conservatives should spend a weekend at Chequers writing out a proposed deal.