Boris Johnson has said public sector workers should be given a pay rise but suggested the move could be paid for by cutting the number of state employees.

The foreign secretary said the minimum wage of £7.50 an hour, which will rise to £9 by 2020, is “not enough”.

He told the Sun: “I want people to be paid more. People get up unbelievably early and they work unbelievably hard, they deserve to be properly paid.”

He added: “You can pay people more, but shrink your wages bill. I’ll be honest with you. I do think you can always find ways of reducing expenditure on things that are not necessary. Any minister who tells you you can’t find savings, it is not true.”

His comments, in advance of the Conservative party’s annual conference – which begins on Sunday in Manchester – are likely to be seen as another challenge to prime minister Theresa May’s authority.

Johnson added: “We brought in a national living wage. I think that is the right thing to do but it is obviously not enough, and I would of course see people getting decently rewarded for their hard work. I really believe in that.”

Johnson called on the Tories to be “more courageous” and “find new ways of invigorating people” about their ideas.

He warned against the Conservative party shifting to the left to attract Labour voters, saying: “It would be a mistake for us to go chasing after Corbyn down some leftist cul de sac.

“He is bathing in this orgiastic adulation from Corbynistas who are conspiring in this myth that he won the election.

“Young people don’t have to go back to the 1970s. You don’t have to time travel, you just have to travel round the world – Venezuela.

“We have got to be engaged mano a mano with all this leftwing nonsense which has been peddled again and we have got to find new ways of invigorating people about our ideas.”