Mr Johnson said a scheme of selling properties through offshore companies to avoid stamp duty was a "scandal".
And he said upgrades to the 150-year-old Tube network were vital to prevent problems five or 10 years down the line.
Shadow chancellor Ed Balls said the Budget must be fair and include measures for jobs and growth.
Asked about the possibility of the 50p top rate tax being axed, he told Sky News' Murnaghan programme no tax was "set in stone".
"You are right to say those with the broadest shoulders should bear the burden and it is also right to say that no tax rate should be set in stone," he said.
"If, in the coming years, we can move on that as a country, fine.
"But do we really think families on £150,000 plus are the first priority?"
Labour is calling on Mr Osborne to cancel measures coming into force in April that will see around 200,000 working parents lose up to £4,000 in working tax credits.
It will also use its Opposition Day debate in the House of Commons next week to demand an urgent review of child benefit reforms, which would see earners on more than £42,476 stripped of their payments, due to come into effect in January 2013.
Mr Balls added: "I think the VAT cut is the best but I think a personal allowance rise, a cut in fuel duty, those things would make sense.
"Osborne and Nick Clegg seem to be saying, they are telling the newspapers, if they can find a way to make the mansion tax work - in the past I've supported that - if George Osborne can make a mansion tax work on multi-million pound properties, fine."