John McDonnell accused the Conservative government of preventing working people from lifting themselves out of poverty by undermining trade unions.
The Labour shadow chancellor made his comments after making an unannounced appearance at a debate at the Glastonbury Festival on Sunday.
Mr McDonnell said a Labour government would both “fulfil the promise” of former Labour leader John Smith that every worker would have trade union rights from day one of employment, and would also restore sectoral collective bargaining.
Collective bargaining sees trade unions negotiate industry-wide agreements for levels of pay and working terms and conditions.
Mr McDonnell, speaking at Glastonbury Festival’s Left Stage, said: “If anyone says why is that important, we have 4.5 million children in this country living in poverty. The prediction if the Tories remain in office within a short time will be five million.
“Two thirds of those kids live in families where someone is at work. What does that say? That says that pay is so low that it cannot actually lift people out of poverty. These Tories have broken the link between work and actually being able to lift yourself out of poverty.
“If you don’t believe me read the United Nations’ rapporteurs report. This is first time it’s ever happened in our history, that the UN has sent a rapporteur into this county to report on levels of poverty and wealth and the grotesque levels of inequality.
“what he reports on is not poverty, he says it’s destitution that we now have in our society, and that’s a result of the undermining of trade union rights, the undermining of collective bargaining, and as a result of that the undermining of basic wages.”
