LONDON - Liz Truss, the British prime minister, campaigned as a tax cutter and a champion of supply-side economics. Having now delivered that free-market agenda — the tax cuts and deregulatory plans that have stunned financial markets — her political future hangs in the balance. In the latest polls, the opposition Labour Party has taken a lead of 17 percentage points over Truss’s Tories.

Labour is seizing the moment to present itself as the party of fiscal responsibility. As some experts predicted that the pound could tumble further, economists and analysts said that uncertainty over Britain’s economic path would continue to hang over the markets and Truss’s government.

The British government has proposed cutting taxes at a time of near-double-digit inflation, as well as making the unexpected decision to abolish the top income tax rate. The chancellor of the Exchequer, Kwasi Kwarteng, did not submit the package to the scrutiny a government budget normally receives, deepening fears that the tax cuts would blow a hole in Britain’s public finances. The International Monetary Fund has urged the government to reconsider.

The pound stabilized briefly against the dollar yesterday, as did 10-year rates on British government bonds, though both began to gyrate later in the day after a senior official at the Bank of England signalled an aggressive increase in interest rates.

The Bank of England’s chief economist offered a first glimpse into how the bank would assess the government’s sweeping package of tax cuts, borrowing and spending.