In stark contrast to opinion polls that have until the past week shown May on course for a big win in the snap election she called, the YouGov model suggested May would lose 20 seats and her 17-seat working majority in the 650-seat British Parliament, Reuters reported.
The YouGov constituency projection, based on 50,000 interviews over the course of a week, showed May would win 310 seats, down from the 331 seats won by her predecessor David Cameron in 2015.
The opposition Labour Party could win 257 seats, up from 232 seats in 2015, YouGov said. Smaller parties, including the Scottish National Party and Northern Irish parties, could win 83 seats, The Times newspaper quoted YouGov as predicting.
If the YouGov model turns out to be accurate, May would be well short of the 326 seats needed to form a government in June, when formal Brexit negotiations are due to begin.
May called the snap election in a bid to strengthen her hand in negotiations on Britain's exit from the European Union, to win more time to deal with the impact of the divorce and to strengthen her grip on the Conservative Party.
But if she does not handsomely beat the 12-seat majority Cameron won in 2015, her electoral gamble will have failed and her authority could be undermined just as she tries to deliver what she has told voters will be a successful Brexit.