Chancellor Philip Hammond has signalled he will prioritise building up a Brexit safety net fund ahead of launching a spending spree in Wednesday's Budget.
Facing opposition calls to use an unexpected rise in tax receipts to pump more money into services and infrastructure, Mr Hammond made it clear he wanted to ensure the country had enough resources in reserve to cope with any Brexit turbulence over the next two years.
Amid reports that he was planning to raise some taxes in the Budget rather than loosen public purse strings, the Chancellor stressed the need for caution as the UK prepared to trigger two years of testing Brexit negotiations with the EU by invoking Article 50 of the Lisbon Treaty.
Praising the economy's "resilience" in the face of some gloomy post-Brexit referendum forecasts, Mr Hammond made it clear he was not prepared to take risks as the UK embarked in a new direction.
He told the BBC: "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's comments came as he faced mounting pressure to deal with the situation in social care for the elderly, and soothe the Tory backlash against changes to business rates.
The Chancellor is expected to announce a £500 million boost to British science and innovation in the Budget.
Shadow chancellor John McDonnell accused the Tories of not being prepared to deal with the scope of the mounting crisis in social care and the NHS.