Britain will hold an emergency budget in the autumn and hopes a faster growing economy will allow it to pay for spending pledges, a junior interior minister said on Friday.

Prime Minister Boris Johnson took office on Wednesday promising a raft of spending pledges including increasing police numbers by 20,000 to help cut crime.

"The prime minister has also announced there's going to be an emergency budget in the autumn which will be designed to stimulate the economy," Kit Malthouse told.

"What you hope is that a more strongly growing economy will produce greater tax revenue which we can pay for some of the things that we want to do," he said.

Malthouse said a pledge to boost police numbers would cost about 500 million pounds in the first year.