The police response to the Manchester Arena bombing was "grossly deficient", lawyers for the 22 bereaved families have said.
Pete Weatherby QC told the public inquiry into the May 2017 terror attack there was a command vacuum at Greater Manchester Police and that the force's senior leadership team were largely responsible for institutional failure.
He made the remarks as part of closing submissions on the emergency response to the suicide bombing by Salman Abedi in the venue's City Room foyer following the end of an Ariana Grande concert.
Pete Weatherby QC added, "Greater Manchester Police were not wholly responsible for the emergency response failures but they were at the centre, and without GMP establishing the basics it was always going to be difficult for other agencies to respond effectively."
The inquiry has heard that GMP's force duty officer (FDO) on the night declared an Operation Plato incident - to signal a marauding terrorist firearms attack - but did not inform the other blue light emergency services.
Mr Weatherby said: "The failure to communicate with the other emergency services meant that joined-up multi-agency working between police, ambulance and fire and rescue did not get to first base, which was a shared understanding of an evolving incident. This was compounded by a failure to declare a major incident."
Armed officers entered the City Room and determined there was no ongoing firearms threat - amid erroneous reports of shooting - and found no evidence of a secondary device.
However, he said, a "key failure" followed in that other emergency responders were not told it was safe to go into the casualty zone.
He said GMP was aware of the "very longstanding problem" which became the single point of failure on the night - the overloading and overwhelming of the FDO role - but had failed to address it prior to the bombing.
GMP's planning for such incidents was "haphazard and inadequate" with no obvious overall control of policies and plans, he said, while a "grossly inaccurate picture" was presented to the independent Kerslake Review some 10 months after the attack.
Mr Weatherby highlighted a letter signed by former Chief Constable Ian Hopkins which stated that GMP's emergency response was not only competent but exemplary.
But Mr Hopkins later conceded to the inquiry it was a "grave error" that the letter wrongly asserted that other emergency services had been informed about Operation Plato without any delay.
Mr Weatherby said: "The very uncomfortable reality is either the Chief Constable and his senior leadership team and advisers were consciously misleading Lord Kerslake or 10 months on they really had no idea of what had gone wrong."