Jeremy Corbyn has said Labour will "take on the establishment" in 2017 and not "stand by" as Theresa May negotiates a Brexit deal that only protects "the bankers in the City".
The Labour leader said in his New Year's message he "understood" the Brexit vote showed "people didn't trust" politicians or the European Union and promised his party would not try to block the referendum result.
Addressing the prospect of a post-EU deal, he said: "A Brexit that protects the bankers in the City and continues to give corporate handouts to the biggest companies is not good enough."
Mr Corbyn said he blamed the political system for "letting down the people of this country" and said "decisions made in Westminster are making people's lives harder".
The Labour leader said his political career underlined his credentials as the man to take on the government.
"I've spent over 40 years in politics campaigning for a better way of doing things, standing up for people, taking on the establishment and opposing decisions that would make us worse-off," he said.
Mr Corbyn used his message to attack Theresa May's administration, saying its actions had left the NHS and social care system at "breaking point" and "priced out" homeless families from a housing market that "only works for the few".
"Those in charge today have put the jobs market, housing, the NHS and social care in crisis," he said. "We can't let them mess this up. It's about everyone's future."
Mr Corbyn said insecure housing and insecure work had left millions of Britons struggling.
"Millions of people can't plan their lives because, whether on temporary or zero-hours contracts, they don't know what job or what hours they'll have from day to day, week to week or month to month", he said. "For many, pay is so low that it doesn't make ends meet."