It is a "moral imperative" for people to pay their "fair share" of tax, Jeremy Corbyn has said as he warned that vital public services are threatened by a lack of resources.
The Labour leader said his message to the middle classes was that they too would need the NHS and must be prepared to fund it.
Mr Corbyn said the Government was "hanging on by a thread" and his party was ready for another election - but he acknowledged "we must do more to broaden our appeal".
In an interview with the Sunday Mirror, he defended Labour's plans to hike income tax for the wealthy.
"We must all pay our fair share," he said, adding: "There's a moral imperative. We will raise tax at the top end in order to invest for the rest of society. I want to lead a Labour government that will do that."
At the general election, Labour set out plans for the threshold at which people start paying the 45p rate of income tax to be reduced to £80,000 from £150,000, with a new 50p rate for people earning more than £123,000.
Explaining why extra funding was required, Mr Corbyn said: "I do say to the middle classes and the well-off, one day you will be ill. You'll need the NHS.
"And your kids may not be able to buy a house. They're not going to get a council place because they're not in desperate need. Think about it. Are we a society that houses everybody? Or are we going to be a society that is the lowest-paid, worst housed, most indebted country in Europe? Because that's where we're heading at the moment."
Mr Corbyn also said it was "incredibly reprehensible" to attempt to dodge taxes by putting money in offshore havens.
"There are very large amounts that don't appear on the books and are in tax havens or in evasion strategies. It is incredibly reprehensible to make vast sums then shift the profits elsewhere. If we don't deal with evasion on this industrial scale then we all lose out.
"The blunt point I would make to the very wealthy who think it is clever to avoid taxation is what happens if your house catches fire and who pays for the fire engine? Or you might suffer a heart attack and be waiting for an ambulance because there aren't enough resources."
Mr Corbyn said Labour was "ready to have an election at any point" if Theresa May's administration collapsed and he was "relishing the opportunity to campaign across the country with our message of hope".
He said Labour had to build on June's election, adding: "Winning 13 million votes was a great achievement, but there's more convincing to be done."