A plan to merge National Insurance (NI) with income tax would increase wages, create jobs and help reduce costs, business leaders have said.
A report is calling for the 40p income tax threshold to be raised to stop hundreds of thousands of extra people falling into the bracket.
Treasury minister David Gauke has said it is "morally wrong" to pay tradesmen in cash, in the hope of avoiding tax.
The government has launched an online tax calculator enabling people to work out how much tax they have paid and how it is spent.
The UK should introduce a single income tax of 30% as part of a radical reform of the taxation system designed to boost economic growth, an influential committee has said.
Chancellor George Osborne has played down plans to limit tax relief for charitable giving.
Labour has been defeated in its efforts to block controversial plans to freeze age-related income tax allowances for pensioners.
Almost one in ten people earning over £10m per year pays less than the 20% basic rate of income tax, according to Treasury figures.