Planned benefit cuts by the Conservative government combined with soaring inflation will leave nearly 3 million working households an average of £2,500 a year worse off, according to analysis by the Institute of Fiscal Studies.
Low inflation over the last two years has meant the government's freeze on most working-age benefits has only amounted to a 1% real cut so far.
But rising inflation from the falling pound is now set to reduce the value of these benefits by 5% between now and 2020, with total cuts of over £5 billion a year in the long run.
Liberal Democrat Shadow Chancellor Susan Kramer commented: "Theresa May’s plans for a divisive Hard Brexit and savage cuts to benefits will leave millions of working families worse off.
"Three million households will be hit to the tune of £2,500 a year as a result of cuts to tax credits, rising prices and the falling pound.
"The Brexit squeeze will hit people in the pocket across the country, with the poorest families hit hardest.
"This election is a chance to change Britain's future and stop a disastrous hard Brexit that will leave us all poorer.
"Every Liberal Democrat MP elected is a challenge to Theresa May’s Hard Brexit agenda."