The Labour Party is predicted to win 261 seats, up from 257 projected on Friday.
However, Theresa May's personal approval rating has become negative for the first time since she became prime minister in July 2016, a fresh ComRes poll showed on Saturday.
The survey, conducted for the Sunday Mirror and Independent newspapers, revealed that 42 percent of respondents had an unfavorable opinion about May, a rise of 10 points since the last Favourability Index in February, while 39 percent had opposite views.
According to the poll, carried out online between May 31 and June 2 among 2,038 people, the Tories are now up one point on 47 percent and Labour, also up one point, on 35 percent.
On April 18, UK Prime Minister Theresa May announced her decision to hold an early parliamentary election on June 8 to overcome divisions in the parliament and succeed in negotiations with the European Union on Brexit.