Last year, Liam Fox, the former Defence Secretary, called on George Osborne to drop the ring-fencing of the schools, health and overseas aid budgets and last week the former Scottish GP urged the Chancellor to withdraw special protection from the "wasteful NHS".
Despite the squeeze on spending, David Cameron has singled out schools, health and aid for budget ring-fencing. But with the Chancellor announcing a future Tory government would seek another £25 billion in cuts - half from welfare - departments would be called on to make deeper cuts in the years ahead.
While Mr Johnson said Mr Osborne was right to say more needed to be done to reduce Britain's budget deficit, he added: "(Ministers) should be looking at all areas of public spending.
"I am still slighty perplexed about why we contribute aid money to some of these countries that are on the path of prosperity."
Following his announcement of £25bn of future cuts, the Chancellor was accused of "hacking at the same people" by allies of Iain Duncan Smith, the Work and Pensions Secretary, who is said to be worried about the impact yet more planned cuts would have on the poorest in society.
Meanwhile, the London Mayor continued his war of words with the Deputy Prime Minister on his weekly radio show.
Mr Johnson declared: "I don't want to get into some sort of endless ding-dong with poor old Cleggers.
"He's there to fulfil a very important ceremonial function as David Cameron's lapdog-cum-prophylactic protection device for all the difficult things that David Cameron has to do that cheese off the rest."
Mr Clegg hit back via a close source, who said: "Boris needs to make up his mind. Half the time he's moaning that we are blocking policies and half the time we're a lapdog." Elsewhere, as the political fall-out to Mr Osborne's warning about more cuts under a future Conservative government continued, a ComRes poll showed growing public confidence about the UK economy.
Some 36% of Britons said it had improved in the last three months - the highest figure since the question was first asked when polling began in October 2010.
In contrast, 30% said it had got worse - a joint-record low.