John McDonnell, the shadow chancellor, has claimed that the victims of the Grenfell Tower fire were “murdered by political decisions”, saying politicians’ decisions over recent decades were important factors in the deaths of 79 people in the tower block in north Kensington, London.

Addressing a debate on Sunday at the Glastonbury festival, in Somerset, chaired by the Guardian’s John Harris, McDonnell said: “Is democracy working? It didn’t work if you were a family living on the 20th floor of Grenfell Tower. Those families, those individuals – 79 so far and there will be more – were murdered by political decisions that were taken over recent decades.”

The strength of the language used by the MP, whose Hayes and Harlington constituency is a few miles from the site of the tower block fire, will anger some Conservative MPs who have accused Labour of trying to politicise a disaster.

McDonnell added that housing provision was now driven by profitability instead of need. “The decisions not to build homes and to view housing as only for financial speculation rather than for meeting a basic human need, made by politicians over decades, murdered those families,” he said. “The decision to close fire stations and to cut 10,000 firefighters and then to freeze their pay for over a decade contributed to those deaths inevitably and they were political decisions.”

McDonnell’s intervention came amid continuing tension in Camden, north London, where the local council is trying to persuade remaining residents to leave their homes in tower blocks where most have been evacuated.

Thousands of residents have left their homes on the Chalcots estate after an evacuation operation which began Friday to clear the buildings because of an “unacceptable fire risk”. Some residents said they had been intimidated by security guards.

The effort to clear the estate comes after the government revealed that all of the 34 high-rises that submitted building cladding samples for inspection after the Grenfell Tower disaster failed combustibility tests. Hundreds more blocks have still to be tested.

The Glastonbury debate took place on Sunday in the Left Field a day after Labour’s leader, Jeremy Corbyn, drew a crowd of thousands to the Pyramid stage. McDonnell appeared with the Green party’s co-leader Jonathan Bartley, and Faiza Shaheen, an economist.

McDonnell’s words echoed the claims of the Labour MP Diane Abbott, who told a Progress meeting on Saturday that the final death toll from the Grenfell Tower would exceed 100 and blamed the disaster on Conservative attitudes towards social housing.

She said: “The Tories think people in social housing are second-class citizens. And, as we have seen from Grenfell [Tower], they are offering them second-class standards of safety. So, a direct consequence of that, a direct consequence of outsourcing … and a direct consequence of deregulation.”

McDonnell repeatedly drew cheers from the crowds when he spoke of the need for electoral reform and changes to the House of Lords. He called for a “progressive intellectual alliance” between parties to rebuild what was needed for a democracy. “The House of Lords – 92 of them are there on the basis of who Charles II shagged at some point in the past,” he said. “It can’t be right that we have a House of Lords that’s based upon those people appointed rather than elected.”

McDonnell told the audience: “We have been beating our heads against a brick wall for 30 years,” he said. “We are on the edge of a huge victory.”

McDonnell said he and Corbyn had been trying to achieve honest politics for the past two years despite media attacks. He said some sections of the press “came after us and tried to destroy us because we stood up to the establishment and the elite”.