Britain’s Conservative party will win a “Margaret Thatcher style” landslide in next month’s national election unless the Labour party improves its poll ratings, according to Tom Watson, Labour’s deputy leader.

In an interview with The Guardian newspaper published on Saturday, Watson said Labour had “a mountain to climb” before election day.

“If we get to June 8 and (Conservative leader Theresa May) still commands the lead in the polls she had at the start of the election, she will command a Margaret Thatcher style majority,” said Watson, referring to the 140- and 100-seat landslides the Conservatives won in 1983 and 1987.

“A Conservative government with a 100 majority is what it is. It will be very hard for them to be held to account in the House of Commons. It means there won’t be the usual checks and balances of democracy … all those things go out the window.”