Chancellor Philip Hammond has signalled he will take a cautious approach to spending in Wednesday's Budget.
Mr Hammond accused people calling for him to use increased tax receipts for a major injection of cash into the economy and services as "reckless".
He told the BBC's Andrew Marr Show: "It's not money in the wallet because we are borrowing a huge amount of money. Remember, we have over £1.7 trillion worth of debt. This isn't money in a pot. What is being speculated on is whether we might not have borrowed quite as much as we were forecast to borrow.
"If your bank increases your credit card limit, I don't think you feel obliged to go out and spend every last penny of it immediately."
Mr Hammond said he saw his role as ensuring "that we have got reserves in the tank, so as we embark on the journey that we will be taking over the next couple of years, we are confident that we have got enough gas in the tank to see us through that journey".
Amid reports that the Chancellor was set to provide more than £1 billion for social care in the Budget, Mr Hammond said: "I recognise in particular that social care, and local authorities delivering social care are under some pressure. This isn't just about money. We should remember there are many authorities managing extremely well."
The Chancellor rejected calls from Labour's John McDonnell for him to publish his tax returns.
"No. I have no intention of doing so. Just for the record my tax affairs are all perfectly regular and up to date. But I think this demonstration politics isn't helping the atmosphere in British politics."