(FORTUNE Magazine) – With angry demonstrations against a controversial new personal tax sweeping Britain, support for Margaret Thatcher has sunk to its lowest since she became Prime Minister in 1979. Polls show her Conservatives 19% behind Labour, and up to a third of Tory Members of Parliament say she should resign before the next general election, which must be held by mid-1992. Thatcher has been down before, only to bounce back to resounding triumph. But this bout is her worst, and her troubles have produced a stunning reversal for Labour and its leader, Neil Kinnock. What would Britain be like under a Labour government, especially for business? Probably not much different from now. Labour might try to ease money a little, though it would be under City pressure to fight inflation. Kinnock's government would likely resemble those of the moderate pro-business socialists in France and Spain. Since he has distanced himself from his party's radicals, renationalization would not be part of his vision.