LONDON (Reuters) - Britain's opposition Labour Party is on track to win the most seats in the party's history at a July 4 election, according to a YouGov poll published on Wednesday.

The multilevel regression and post-stratification (MRP) poll predicted that Labour would win 425 seats, with Prime Minister Rishi Sunak's Conservatives expected to win 108. Nigel Farage's Reform UK was set to win 5 seats, it forecast.

That would give Labour a majority of 200, it said. The poll was carried out June 11-18, with YouGov speaking to nearly 40,000 voters.

That compared to a prediction of 422 seats for Labour and 140 for the Conservatives at its last MRP poll, published earlier this month before Farage entered the race.

(Reporting by Kylie MacLellan; Editing by Sachin Ravikumar)