Party leaders have returned to the campaign trail amid opposition fears of a Conservative landslide after the Tories made sweeping gains in the local elections.
The Liberal Democrats are seeking to regain the electoral initiative with their "flagship" plan to put a penny on income tax to raise £6 billion-a-year for the NHS and social care.
Leader Tim Farron said: "Theresa May doesn't care about the NHS or social care. People are lying on trolleys in hospital corridors and she has done nothing.
"The Liberal Democrats will rescue the NHS and social care. We are prepared to be honest with people and say that we will all need to chip in a little more."
Speaking at a GP surgery in south London on Saturday, Mr Farron later said: "Everybody else is pretending it can be done on the cheap, it cannot be done on the cheap.
He said it would cost individuals an average £3 a week for an average income earner to "secure the best health, the best care, for your loved ones throughout the whole of their lives".
The Lib Dems' health spokesman Norman Lamb said: "This pledge is the first step in restoring it to where it should be. A penny on the pound to save the NHS is money well spent in our view."
Reacting to the announcement, the Conservatives said that all the main opposition parties were now committed to raising taxes.
Treasury minister Jane Ellison said: "A vote for anyone other than Theresa May means you will pay more tax.
"Jeremy Corbyn, the Lib Dems and SNP will hit 30 million people in the pocket with higher income taxes."
- Corbyn concedes Labour face 'historic' task
Meanwhile, Jeremy Corbyn has admitted Labour faces a task on a "historic scale" if it is to regain power in the General Election after losing more than 300 councillors in local elections.
Mr Corbyn acknowledged that Labour had lost "too many" councillors and now faced a mammoth job if he is to gain the keys of No 10.
"We have five weeks to win the General Election so we can fundamentally transform Britain for the many not the few," he said in a statement.
"We know this is no small task, it is a challenge on an historic scale."
And with the Conservatives gaining more than 500 councillors, as well as winning tightly-fought mayoral races in the West Midlands and Tees Valley, Theresa May insists she is taking "nothing for granted".